diff --git a/.ts-eslintrc.js b/.ts-eslintrc.js
index ac73bb34..ae7233ed 100644
--- a/.ts-eslintrc.js
+++ b/.ts-eslintrc.js
@@ -20,8 +20,10 @@ module.exports = {
     rules: {
         "@typescript-eslint/no-floating-promises": 2,
         "@typescript-eslint/no-misused-promises": 2,
-        'no-unused-vars': 'off',
-        '@typescript-eslint/no-unused-vars': ['warn'],
-        'no-undef': 'off',
+        "no-unused-vars": "off",
+        "@typescript-eslint/no-unused-vars": ["warn"],
+        "no-undef": "off",
+        "semi": ["error", "always"],
+        "@typescript-eslint/explicit-function-return-type": ["error"]
     }
 };
diff --git a/src/observable/BaseObservable.ts b/src/observable/BaseObservable.ts
index 11ecd8a0..edbdd8bc 100644
--- a/src/observable/BaseObservable.ts
+++ b/src/observable/BaseObservable.ts
@@ -34,7 +34,7 @@ export abstract class BaseObservable<T> {
         if (this._handlers.size === 1) {
             this.onSubscribeFirst();
         }
-        return () => {
+        return (): undefined => {
             return this.unsubscribe(handler);
         };
     }
@@ -63,17 +63,18 @@ export abstract class BaseObservable<T> {
     // Add iterator over handlers here
 }
 
+// eslint-disable-next-line @typescript-eslint/explicit-function-return-type
 export function tests() {
     class Collection extends BaseObservable<{}> {
         firstSubscribeCalls: number = 0;
         firstUnsubscribeCalls: number = 0;
 
-        onSubscribeFirst() { this.firstSubscribeCalls += 1; }
-        onUnsubscribeLast() { this.firstUnsubscribeCalls += 1; }
+        onSubscribeFirst(): void { this.firstSubscribeCalls += 1; }
+        onUnsubscribeLast(): void { this.firstUnsubscribeCalls += 1; }
     }
 
     return {
-        test_unsubscribe(assert) {
+        test_unsubscribe(assert): void {
             const c = new Collection();
             const unsubscribe = c.subscribe({});
             unsubscribe();
diff --git a/src/observable/ObservableValue.ts b/src/observable/ObservableValue.ts
index dab8fb52..96791f91 100644
--- a/src/observable/ObservableValue.ts
+++ b/src/observable/ObservableValue.ts
@@ -20,7 +20,7 @@ import type {SubscriptionHandle} from "./BaseObservable";
 
 // like an EventEmitter, but doesn't have an event type
 export abstract class BaseObservableValue<T> extends BaseObservable<(value: T) => void> {
-    emit(argument: T) {
+    emit(argument: T): void {
         for (const h of this._handlers) {
             h(argument);
         }
@@ -68,7 +68,7 @@ class WaitForHandle<T> implements IWaitHandle<T> {
         return this._promise;
     }
 
-    dispose() {
+    dispose(): void {
         if (this._subscription) {
             this._subscription();
             this._subscription = null;
@@ -82,7 +82,7 @@ class WaitForHandle<T> implements IWaitHandle<T> {
 
 class ResolvedWaitForHandle<T> implements IWaitHandle<T> {
     constructor(public promise: Promise<T>) {}
-    dispose() {}
+    dispose(): void {}
 }
 
 export class ObservableValue<T> extends BaseObservableValue<T> {
@@ -113,7 +113,7 @@ export class RetainedObservableValue<T> extends ObservableValue<T> {
         this._freeCallback = freeCallback;
     }
 
-    onUnsubscribeLast() {
+    onUnsubscribeLast(): void {
         super.onUnsubscribeLast();
         this._freeCallback();
     }
@@ -130,7 +130,7 @@ export class FlatMapObservableValue<P, C> extends BaseObservableValue<C | undefi
         super();
     }
 
-    onUnsubscribeLast() {
+    onUnsubscribeLast(): void {
         super.onUnsubscribeLast();
         this.sourceSubscription = this.sourceSubscription!();
         if (this.targetSubscription) {
@@ -138,7 +138,7 @@ export class FlatMapObservableValue<P, C> extends BaseObservableValue<C | undefi
         }
     }
 
-    onSubscribeFirst() {
+    onSubscribeFirst(): void {
         super.onSubscribeFirst();
         this.sourceSubscription = this.source.subscribe(() => {
             this.updateTargetSubscription();
@@ -147,7 +147,7 @@ export class FlatMapObservableValue<P, C> extends BaseObservableValue<C | undefi
         this.updateTargetSubscription();
     }
 
-    private updateTargetSubscription() {
+    private updateTargetSubscription(): void {
         const sourceValue = this.source.get();
         if (sourceValue) {
             const target = this.mapper(sourceValue);
@@ -174,9 +174,10 @@ export class FlatMapObservableValue<P, C> extends BaseObservableValue<C | undefi
     }
 }
 
+// eslint-disable-next-line @typescript-eslint/explicit-function-return-type
 export function tests() {
     return {
-        "set emits an update": assert => {
+        "set emits an update": (assert): void => {
             const a = new ObservableValue<number>(0);
             let fired = false;
             const subscription = a.subscribe(v => {
@@ -187,7 +188,7 @@ export function tests() {
             assert(fired);
             subscription();
         },
-        "set doesn't emit if value hasn't changed": assert => {
+        "set doesn't emit if value hasn't changed": (assert): void => {
             const a = new ObservableValue(5);
             let fired = false;
             const subscription = a.subscribe(() => {
@@ -198,7 +199,7 @@ export function tests() {
             assert(!fired);
             subscription();
         },
-        "waitFor promise resolves on matching update": async assert => {
+        "waitFor promise resolves on matching update": async (assert): Promise<void> => {
             const a = new ObservableValue(5);
             const handle = a.waitFor(v => v === 6);
             await Promise.resolve().then(() => {
@@ -207,7 +208,7 @@ export function tests() {
             await handle.promise;
             assert.strictEqual(a.get(), 6);
         },
-        "waitFor promise rejects when disposed": async assert => {
+        "waitFor promise rejects when disposed": async (assert): Promise<void> => {
             const a = new ObservableValue<number>(0);
             const handle = a.waitFor(() => false);
             await Promise.resolve().then(() => {
@@ -215,7 +216,7 @@ export function tests() {
             });
             await assert.rejects(handle.promise, AbortError);
         },
-        "flatMap.get": assert => {
+        "flatMap.get": (assert): void => {
             const a = new ObservableValue<undefined | {count: ObservableValue<number>}>(undefined);
             const countProxy = a.flatMap(a => a!.count);
             assert.strictEqual(countProxy.get(), undefined);
@@ -223,7 +224,7 @@ export function tests() {
             a.set({count});
             assert.strictEqual(countProxy.get(), 0);
         },
-        "flatMap update from source": assert => {
+        "flatMap update from source": (assert): void => {
             const a = new ObservableValue<undefined | {count: ObservableValue<number>}>(undefined);
             const updates: (number | undefined)[] = [];
             a.flatMap(a => a!.count).subscribe(count => {
@@ -233,7 +234,7 @@ export function tests() {
             a.set({count});
             assert.deepEqual(updates, [0]);
         },
-        "flatMap update from target": assert => {
+        "flatMap update from target": (assert): void => {
             const a = new ObservableValue<undefined | {count: ObservableValue<number>}>(undefined);
             const updates: (number | undefined)[] = [];
             a.flatMap(a => a!.count).subscribe(count => {
diff --git a/src/observable/list/AsyncMappedList.ts b/src/observable/list/AsyncMappedList.ts
index 53edde21..f1785c13 100644
--- a/src/observable/list/AsyncMappedList.ts
+++ b/src/observable/list/AsyncMappedList.ts
@@ -135,10 +135,12 @@ class ResetEvent<F> {
 import {ObservableArray} from "./ObservableArray";
 import {ListObserver} from "../../mocks/ListObserver.js";
 
+
+// eslint-disable-next-line @typescript-eslint/explicit-function-return-type
 export function tests() {
     return {
-        "events are emitted in order": async assert => {
-            const double = n => n * n;
+        "events are emitted in order": async (assert): Promise<void> => {
+            const double = (n: number): number => n * n;
             const source = new ObservableArray<number>();
             const mapper = new AsyncMappedList(source, async n => {
                 await new Promise(r => setTimeout(r, n));
diff --git a/src/observable/list/BaseMappedList.ts b/src/observable/list/BaseMappedList.ts
index 4e3d05e0..0435a760 100644
--- a/src/observable/list/BaseMappedList.ts
+++ b/src/observable/list/BaseMappedList.ts
@@ -37,14 +37,15 @@ export class BaseMappedList<F,T,R = T> extends BaseObservableList<T> {
         this._removeCallback = removeCallback;
     }
 
-    findAndUpdate(predicate: (value: T) => boolean, updater: (value: T) => any | false) {
+    findAndUpdate(predicate: (value: T) => boolean, updater: (value: T) => any | false): boolean {
         return findAndUpdateInArray(predicate, this._mappedValues!, this, updater);
     }
 
-    get length() {
+    get length(): number {
         return this._mappedValues!.length;
     }
 
+    // eslint-disable-next-line @typescript-eslint/explicit-function-return-type
     [Symbol.iterator]() {
         return this._mappedValues!.values();
     }
diff --git a/src/observable/list/BaseObservableList.ts b/src/observable/list/BaseObservableList.ts
index e2806c72..1fd82c25 100644
--- a/src/observable/list/BaseObservableList.ts
+++ b/src/observable/list/BaseObservableList.ts
@@ -26,17 +26,17 @@ export interface IListObserver<T> {
 
 export function defaultObserverWith<T>(overrides: { [key in keyof IListObserver<T>]?: IListObserver<T>[key] }): IListObserver<T> {
     const defaults = {
-        onReset(){},
-        onAdd(){},
-        onUpdate(){},
-        onRemove(){},
-        onMove(){},
+        onReset(): void {},
+        onAdd(): void {},
+        onUpdate(): void {},
+        onRemove(): void {},
+        onMove(): void {},
     };
     return Object.assign(defaults, overrides);
 }
 
 export abstract class BaseObservableList<T> extends BaseObservable<IListObserver<T>> implements Iterable<T> {
-    emitReset() {
+    emitReset(): void {
         for(let h of this._handlers) {
             h.onReset(this);
         }
diff --git a/src/observable/list/ConcatList.ts b/src/observable/list/ConcatList.ts
index 8ef7326c..aaad5a6a 100644
--- a/src/observable/list/ConcatList.ts
+++ b/src/observable/list/ConcatList.ts
@@ -86,10 +86,12 @@ export class ConcatList<T> extends BaseObservableList<T> implements IListObserve
         return len;
     }
 
+    // eslint-disable-next-line @typescript-eslint/explicit-function-return-type
     [Symbol.iterator]() {
         let sourceListIdx = 0;
         let it = this._sourceLists[0][Symbol.iterator]();
         return {
+            // eslint-disable-next-line @typescript-eslint/explicit-function-return-type
             next: () => {
                 let result = it.next();
                 while (result.done) {
@@ -108,16 +110,19 @@ export class ConcatList<T> extends BaseObservableList<T> implements IListObserve
 
 import {ObservableArray} from "./ObservableArray";
 import {defaultObserverWith} from "./BaseObservableList";
+
+
+// eslint-disable-next-line @typescript-eslint/explicit-function-return-type
 export async function tests() {
     return {
-        test_length(assert) {
+        test_length(assert): void {
             const all = new ConcatList(
                 new ObservableArray([1, 2, 3]),
                 new ObservableArray([11, 12, 13])
             );
             assert.equal(all.length, 6);
         },
-        test_iterator(assert) {
+        test_iterator(assert): void {
             const all = new ConcatList(
                 new ObservableArray([1, 2, 3]),
                 new ObservableArray([11, 12, 13])
@@ -131,7 +136,7 @@ export async function tests() {
             assert.equal(it.next().value, 13);
             assert(it.next().done);
         },
-        test_add(assert) {
+        test_add(assert): void {
             const list1 = new ObservableArray([1, 2, 3]);
             const list2 = new ObservableArray([11, 12, 13]);
             const all = new ConcatList(list1, list2);
@@ -146,7 +151,7 @@ export async function tests() {
             list2.insert(1, 11.5);
             assert(fired);
         },
-        test_update(assert) {
+        test_update(assert): void {
             const list1 = new ObservableArray([1, 2, 3]);
             const list2 = new ObservableArray([11, 12, 13]);
             const all = new ConcatList(list1, list2);
diff --git a/src/observable/list/MappedList.ts b/src/observable/list/MappedList.ts
index ebb418d3..2ddae698 100644
--- a/src/observable/list/MappedList.ts
+++ b/src/observable/list/MappedList.ts
@@ -19,7 +19,7 @@ import {IListObserver} from "./BaseObservableList";
 import {BaseMappedList, runAdd, runUpdate, runRemove, runMove, runReset} from "./BaseMappedList";
 
 export class MappedList<F,T> extends BaseMappedList<F,T> implements IListObserver<F> {
-    onSubscribeFirst() {
+    onSubscribeFirst(): void {
         this._sourceUnsubscribe = this._sourceList.subscribe(this);
         this._mappedValues = [];
         for (const item of this._sourceList) {
@@ -61,18 +61,21 @@ import {ObservableArray} from "./ObservableArray";
 import {BaseObservableList} from "./BaseObservableList";
 import {defaultObserverWith} from "./BaseObservableList";
 
+// eslint-disable-next-line @typescript-eslint/explicit-function-return-type
 export async function tests() {
     class MockList extends BaseObservableList<number> {
-        get length() {
+        get length(): 0 {
             return 0;
         }
+
+        // eslint-disable-next-line @typescript-eslint/explicit-function-return-type
         [Symbol.iterator]() {
             return [].values();
         }
     }
 
     return {
-        test_add(assert) {
+        test_add(assert): void {
             const source = new MockList();
             const mapped = new MappedList(source, n => {return {n: n*n};});
             let fired = false;
@@ -87,7 +90,7 @@ export async function tests() {
             assert(fired);
             unsubscribe();
         },
-        test_update(assert) {
+        test_update(assert): void {
             const source = new MockList();
             const mapped = new MappedList<number, { n: number, m?: number }>(
                 source,
@@ -109,7 +112,7 @@ export async function tests() {
             assert(fired);
             unsubscribe();
         },
-        "test findAndUpdate not found": assert => {
+        "test findAndUpdate not found": (assert): void => {
             const source = new ObservableArray([1, 3, 4]);
             const mapped = new MappedList(
                 source,
@@ -123,7 +126,7 @@ export async function tests() {
                 () => assert.fail()
             ), false);
         },
-        "test findAndUpdate found but updater bails out of update": assert => {
+        "test findAndUpdate found but updater bails out of update": (assert): void => {
             const source = new ObservableArray([1, 3, 4]);
             const mapped = new MappedList(
                 source,
@@ -143,7 +146,7 @@ export async function tests() {
             ), true);
             assert.equal(fired, true);
         },
-        "test findAndUpdate emits update": assert => {
+        "test findAndUpdate emits update": (assert): void => {
             const source = new ObservableArray([1, 3, 4]);
             const mapped = new MappedList(
                 source,
@@ -161,6 +164,6 @@ export async function tests() {
             assert.equal(mapped.findAndUpdate(n => n === 9, () => "param"), true);
             assert.equal(fired, true);
         },
-        
+
     };
 }
diff --git a/src/observable/list/ObservableArray.ts b/src/observable/list/ObservableArray.ts
index 0771d0f6..662f715e 100644
--- a/src/observable/list/ObservableArray.ts
+++ b/src/observable/list/ObservableArray.ts
@@ -75,6 +75,7 @@ export class ObservableArray<T> extends BaseObservableList<T> {
         return this._items.length;
     }
 
+    // eslint-disable-next-line @typescript-eslint/explicit-function-return-type
     [Symbol.iterator]() {
         return this._items.values();
     }
diff --git a/src/observable/list/SortedArray.ts b/src/observable/list/SortedArray.ts
index 7df285a5..c956f7b8 100644
--- a/src/observable/list/SortedArray.ts
+++ b/src/observable/list/SortedArray.ts
@@ -112,6 +112,7 @@ export class SortedArray<T> extends BaseObservableList<T> {
         return this._items.length;
     }
 
+    // eslint-disable-next-line @typescript-eslint/explicit-function-return-type
     [Symbol.iterator]() {
         return new Iterator(this);
     }
@@ -127,6 +128,7 @@ class Iterator<T> {
         this._current = null;
     }
 
+    // eslint-disable-next-line @typescript-eslint/explicit-function-return-type
     next() {
         if (this._sortedArray) {
             if (this._current) {
@@ -147,9 +149,10 @@ class Iterator<T> {
     }
 }
 
+// eslint-disable-next-line @typescript-eslint/explicit-function-return-type
 export function tests() {
     return {
-        "setManyUnsorted": assert => {
+        "setManyUnsorted": (assert): void => {
             const sa = new SortedArray<string>((a, b) => a.localeCompare(b));
             sa.setManyUnsorted(["b", "a", "c"]);
             assert.equal(sa.length, 3);
@@ -157,7 +160,7 @@ export function tests() {
             assert.equal(sa.get(1), "b");
             assert.equal(sa.get(2), "c");
         },
-        "_getNext": assert => {
+        "_getNext": (assert): void => {
             const sa = new SortedArray<string>((a, b) => a.localeCompare(b));
             sa.setManyUnsorted(["b", "a", "f"]);
             assert.equal(sa._getNext("a"), "b");
@@ -166,7 +169,7 @@ export function tests() {
             assert.equal(sa._getNext("c"), "f");
             assert.equal(sa._getNext("f"), undefined);
         },
-        "iterator with removals": assert => {
+        "iterator with removals": (assert): void => {
             const queue = new SortedArray<{idx: number}>((a, b) => a.idx - b.idx);
             queue.setManyUnsorted([{idx: 5}, {idx: 3}, {idx: 1}, {idx: 4}, {idx: 2}]);
             const it = queue[Symbol.iterator]();
diff --git a/src/observable/list/common.ts b/src/observable/list/common.ts
index c67a841b..20f3a8bf 100644
--- a/src/observable/list/common.ts
+++ b/src/observable/list/common.ts
@@ -17,7 +17,12 @@ limitations under the License.
 import {BaseObservableList} from "./BaseObservableList";
 
 /* inline update of item in collection backed by array, without replacing the preexising item */
-export function findAndUpdateInArray<T>(predicate: (value: T) => boolean, array: T[], observable: BaseObservableList<T>, updater: (value: T) => any | false) {
+export function findAndUpdateInArray<T>(
+    predicate: (value: T) => boolean,
+    array: T[],
+    observable: BaseObservableList<T>,
+    updater: (value: T) => any | false
+): boolean {
     const index = array.findIndex(predicate);
     if (index !== -1) {
         const value = array[index];
diff --git a/src/observable/map/ApplyMap.ts b/src/observable/map/ApplyMap.ts
index 4dbbc3d3..4d45b519 100644
--- a/src/observable/map/ApplyMap.ts
+++ b/src/observable/map/ApplyMap.ts
@@ -36,42 +36,42 @@ export class ApplyMap<K, V> extends BaseObservableMap<K, V> {
         this._config = config<K, V>();
     }
 
-    hasApply() {
+    hasApply(): boolean {
         return !!this._apply;
     }
 
-    setApply(apply?: Apply<K, V>) {
+    setApply(apply?: Apply<K, V>): void {
         this._apply = apply;
         if (this._apply) {
             this.applyOnce(this._apply);
         }
     }
 
-    applyOnce(apply: Apply<K, V>) {
+    applyOnce(apply: Apply<K, V>): void {
         for (const [key, value] of this._source) {
             apply(key, value);
         }
     }
 
-    onAdd(key: K, value: V) {
+    onAdd(key: K, value: V): void {
         if (this._apply) {
             this._apply(key, value);
         }
         this.emitAdd(key, value);
     }
 
-    onRemove(key: K, value: V) {
+    onRemove(key: K, value: V): void {
         this.emitRemove(key, value);
     }
 
-    onUpdate(key: K, value: V, params: any) {
+    onUpdate(key: K, value: V, params: any): void {
         if (this._apply) {
             this._apply(key, value, params);
         }
         this.emitUpdate(key, value, params);
     }
 
-    onSubscribeFirst() {
+    onSubscribeFirst(): void {
         this._subscription = this._source.subscribe(this);
         if (this._apply) {
             this.applyOnce(this._apply);
@@ -79,27 +79,28 @@ export class ApplyMap<K, V> extends BaseObservableMap<K, V> {
         super.onSubscribeFirst();
     }
 
-    onUnsubscribeLast() {
+    onUnsubscribeLast(): void {
         super.onUnsubscribeLast();
         if (this._subscription) this._subscription = this._subscription();
     }
 
-    onReset() {
+    onReset(): void {
         if (this._apply) {
             this.applyOnce(this._apply);
         }
         this.emitReset();
     }
 
+    // eslint-disable-next-line @typescript-eslint/explicit-function-return-type
     [Symbol.iterator]() {
         return this._source[Symbol.iterator]();
     }
 
-    get size() {
+    get size(): number {
         return this._source.size;
     }
 
-    get(key: K) {
+    get(key: K): V | undefined {
         return this._source.get(key);
     }
 
diff --git a/src/observable/map/BaseObservableMap.ts b/src/observable/map/BaseObservableMap.ts
index d8a7d43b..206770ee 100644
--- a/src/observable/map/BaseObservableMap.ts
+++ b/src/observable/map/BaseObservableMap.ts
@@ -36,26 +36,26 @@ export type BaseObservableMapConfig<K, V> = {
 }
 
 export abstract class BaseObservableMap<K, V> extends BaseObservable<IMapObserver<K, V>> {
-    emitReset() {
+    emitReset(): void {
         for(let h of this._handlers) {
             h.onReset();
         }
     }
     // we need batch events, mostly on index based collection though?
     // maybe we should get started without?
-    emitAdd(key: K, value: V) {
+    emitAdd(key: K, value: V): void {
         for(let h of this._handlers) {
             h.onAdd(key, value);
         }
     }
 
-    emitUpdate(key: K, value: V, params: any) {
+    emitUpdate(key: K, value: V, params: any): void {
         for(let h of this._handlers) {
             h.onUpdate(key, value, params);
         }
     }
 
-    emitRemove(key: K, value: V) {
+    emitRemove(key: K, value: V): void {
         for(let h of this._handlers) {
             h.onRemove(key, value);
         }
diff --git a/src/observable/map/FilteredMap.ts b/src/observable/map/FilteredMap.ts
index 782a67fe..613b1439 100644
--- a/src/observable/map/FilteredMap.ts
+++ b/src/observable/map/FilteredMap.ts
@@ -35,7 +35,7 @@ export class FilteredMap<K, V> extends BaseObservableMap<K, V> {
         this._config = config<K, V>();
     }
 
-    setFilter(filter: Filter<K, V>) {
+    setFilter(filter: Filter<K, V>): void {
         this._filter = filter;
         if (this._subscription) {
             this._reapplyFilter();
@@ -45,7 +45,7 @@ export class FilteredMap<K, V> extends BaseObservableMap<K, V> {
     /**
      * reapply the filter
      */
-    _reapplyFilter(silent = false) {
+    _reapplyFilter(silent = false): void {
         if (this._filter) {
             const oldIncluded = this._included;
             this._included = this._included || new Map();
@@ -71,7 +71,7 @@ export class FilteredMap<K, V> extends BaseObservableMap<K, V> {
         }
     }
 
-    onAdd(key: K, value: V) {
+    onAdd(key: K, value: V): void {
         if (this._filter) {
             if (this._included) {
                 const included = this._filter(value, key);
@@ -86,7 +86,7 @@ export class FilteredMap<K, V> extends BaseObservableMap<K, V> {
         this.emitAdd(key, value);
     }
 
-    onRemove(key: K, value: V) {
+    onRemove(key: K, value: V): void {
         const wasIncluded = !this._filter || this._included?.get(key);
         if (this._included) {
             this._included.delete(key);
@@ -98,7 +98,7 @@ export class FilteredMap<K, V> extends BaseObservableMap<K, V> {
         }
     }
 
-    onUpdate(key: K, value: V, params: any) {
+    onUpdate(key: K, value: V, params: any): void {
         // if an update is emitted while calling source.subscribe() from onSubscribeFirst, ignore it
         if (!this._included) {
             return;
@@ -113,7 +113,7 @@ export class FilteredMap<K, V> extends BaseObservableMap<K, V> {
         }
     }
 
-    _emitForUpdate(wasIncluded: boolean | undefined, isIncluded: boolean, key: K, value: V, params: any = null) {
+    _emitForUpdate(wasIncluded: boolean | undefined, isIncluded: boolean, key: K, value: V, params: any = null): void {
         if (wasIncluded && !isIncluded) {
             this.emitRemove(key, value);
         } else if (!wasIncluded && isIncluded) {
@@ -123,13 +123,13 @@ export class FilteredMap<K, V> extends BaseObservableMap<K, V> {
         }
     }
 
-    onSubscribeFirst() {
+    onSubscribeFirst(): void {
         this._subscription = this._source.subscribe(this);
         this._reapplyFilter(true);
         super.onSubscribeFirst();
     }
 
-    onUnsubscribeLast() {
+    onUnsubscribeLast(): void {
         super.onUnsubscribeLast();
         this._included = undefined;
         if (this._subscription) {
@@ -137,16 +137,17 @@ export class FilteredMap<K, V> extends BaseObservableMap<K, V> {
         }
     }
 
-    onReset() {
+    onReset(): void {
         this._reapplyFilter();
         this.emitReset();
     }
 
+    // eslint-disable-next-line @typescript-eslint/explicit-function-return-type
     [Symbol.iterator]() {
         return new FilterIterator<K, V>(this._source, this._included);
     }
 
-    get size() {
+    get size(): number {
         let count = 0;
         this._included?.forEach(included => {
             if (included) {
@@ -156,7 +157,7 @@ export class FilteredMap<K, V> extends BaseObservableMap<K, V> {
         return count;
     }
 
-    get(key) {
+    get(key): V | undefined{
         const value = this._source.get(key);
         if (value && this._filter(value, key)) {
             return value;
@@ -188,6 +189,7 @@ class FilterIterator<K, V> {
         this._sourceIterator = map[Symbol.iterator]();
     }
 
+    // eslint-disable-next-line @typescript-eslint/explicit-function-return-type
     next() {
         // eslint-disable-next-line no-constant-condition
         while (true) {
@@ -204,9 +206,11 @@ class FilterIterator<K, V> {
 }
 
 import {ObservableMap} from "..";
+
+// eslint-disable-next-line @typescript-eslint/explicit-function-return-type
 export function tests() {
     return {
-        "filter preloaded list": assert => {
+        "filter preloaded list": (assert): void => {
             const source = new ObservableMap();
             source.add("one", 1);
             source.add("two", 2);
@@ -233,17 +237,17 @@ export function tests() {
             assert.deepEqual(it.next().value, ["three", 3]);
             assert.equal(it.next().done, true);
         },
-        // "filter added values": assert => {
+        // "filter added values": (assert): void => {
 
         // },
-        // "filter removed values": assert => {
+        // "filter removed values": (assert): void => {
 
         // },
-        // "filter changed values": assert => {
+        // "filter changed values": (assert): void => {
 
         // },
 
-        "emits must trigger once": assert => {
+        "emits must trigger once": (assert): void => {
             const source = new ObservableMap();
             let count_add = 0, count_update = 0, count_remove = 0;
             source.add("num1", 1);
diff --git a/src/observable/map/JoinedMap.ts b/src/observable/map/JoinedMap.ts
index 2be95bdf..1b145d85 100644
--- a/src/observable/map/JoinedMap.ts
+++ b/src/observable/map/JoinedMap.ts
@@ -33,7 +33,7 @@ export class JoinedMap<K, V> extends BaseObservableMap<K, V> {
         this._config = config<K, V>();
     }
 
-    onAdd(source: BaseObservableMap<K, V>, key: K, value: V) {
+    onAdd(source: BaseObservableMap<K, V>, key: K, value: V): void {
         if (!this._isKeyAtSourceOccluded(source, key)) {
             const occludingValue = this._getValueFromOccludedSources(source, key);
             if (occludingValue !== undefined) {
@@ -45,7 +45,7 @@ export class JoinedMap<K, V> extends BaseObservableMap<K, V> {
         }
     }
 
-    onRemove(source: BaseObservableMap<K, V>, key: K, value: V) {
+    onRemove(source: BaseObservableMap<K, V>, key: K, value: V): void {
         if (!this._isKeyAtSourceOccluded(source, key)) {
             this.emitRemove(key, value);
             const occludedValue = this._getValueFromOccludedSources(source, key);
@@ -57,7 +57,7 @@ export class JoinedMap<K, V> extends BaseObservableMap<K, V> {
         }
     }
 
-    onUpdate(source: BaseObservableMap<K, V>, key: K, value: V, params: any) {
+    onUpdate(source: BaseObservableMap<K, V>, key: K, value: V, params: any): void {
         // if an update is emitted while calling source.subscribe() from onSubscribeFirst, ignore it
         if (!this._subscriptions) {
             return;
@@ -67,16 +67,16 @@ export class JoinedMap<K, V> extends BaseObservableMap<K, V> {
         }
     }
 
-    onReset() {
+    onReset(): void {
         this.emitReset();
     }
 
-    onSubscribeFirst() {
+    onSubscribeFirst(): void {
         this._subscriptions = this._sources.map(source => new SourceSubscriptionHandler(source, this).subscribe());
         super.onSubscribeFirst();
     }
 
-    _isKeyAtSourceOccluded(source: BaseObservableMap<K, V>, key: K) {
+    _isKeyAtSourceOccluded(source: BaseObservableMap<K, V>, key: K): boolean {
         // sources that come first in the sources array can
         // hide the keys in later sources, to prevent events
         // being emitted for the same key and different values,
@@ -91,7 +91,7 @@ export class JoinedMap<K, V> extends BaseObservableMap<K, V> {
     }
 
     // get the value that the given source and key occlude, if any
-    _getValueFromOccludedSources(source: BaseObservableMap<K, V>, key: K) {
+    _getValueFromOccludedSources(source: BaseObservableMap<K, V>, key: K): V | undefined{
         // sources that come first in the sources array can
         // hide the keys in later sources, to prevent events
         // being emitted for the same key and different values,
@@ -107,7 +107,7 @@ export class JoinedMap<K, V> extends BaseObservableMap<K, V> {
         return undefined;
     }
 
-    onUnsubscribeLast() {
+    onUnsubscribeLast(): void {
         super.onUnsubscribeLast();
         if (this._subscriptions) {
             for (const s of this._subscriptions) {
@@ -116,15 +116,16 @@ export class JoinedMap<K, V> extends BaseObservableMap<K, V> {
         }
     }
 
+    // eslint-disable-next-line @typescript-eslint/explicit-function-return-type
     [Symbol.iterator]() {
         return new JoinedIterator<K, V>(this._sources);
     }
 
-    get size() {
+    get size(): number {
         return this._sources.reduce((sum, s) => sum + s.size, 0);
     }
 
-    get(key: K): V | undefined{
+    get(key: K): V | undefined {
         for (const s of this._sources) {
             const value = s.get(key);
             if (value) {
@@ -199,28 +200,28 @@ class SourceSubscriptionHandler<K, V> {
         this._subscription = undefined;
     }
 
-    subscribe() {
+    subscribe(): this {
         this._subscription = this._source.subscribe(this);
         return this;
     }
 
-    dispose() {
+    dispose(): void {
         if (this._subscription) this._subscription = this._subscription();
     }
 
-    onAdd(key: K, value: V) {
+    onAdd(key: K, value: V): void {
         this._joinedMap.onAdd(this._source, key, value);
     }
 
-    onRemove(key: K, value: V) {
+    onRemove(key: K, value: V): void {
         this._joinedMap.onRemove(this._source, key, value);
     }
 
-    onUpdate(key: K, value: V, params: any) {
+    onUpdate(key: K, value: V, params: any): void {
         this._joinedMap.onUpdate(this._source, key, value, params);
     }
 
-    onReset() {
+    onReset(): void {
         this._joinedMap.onReset();
     }
 }
@@ -228,9 +229,9 @@ class SourceSubscriptionHandler<K, V> {
 
 import {ObservableMap} from "..";
 
+// eslint-disable-next-line @typescript-eslint/explicit-function-return-type
 export function tests() {
-
-    function observeMap(map: JoinedMap<any, any>) {
+    function observeMap(map: JoinedMap<any, any>): { type: string; key: any; value: any; params?: any; }[] {
         const events: { type: string, key: any, value: any, params?: any }[] = [];
         map.subscribe({
             onAdd(key, value) { events.push({ type: "add", key, value }); },
@@ -244,7 +245,7 @@ export function tests() {
     }
 
     return {
-        "joined iterator": assert => {
+        "joined iterator": (assert): void => {
             const firstKV: [string, number] = ["a", 1];
             const secondKV: [string, number] = ["b", 2];
             const thirdKV: [string, number] = ["c", 3];
@@ -254,7 +255,7 @@ export function tests() {
             assert.equal(it.next().value, thirdKV);
             assert.equal(it.next().done, true);
         },
-        "prevent key collision during iteration": assert => {
+        "prevent key collision during iteration": (assert): void => {
             const first = new ObservableMap();
             const second = new ObservableMap();
             const join = new JoinedMap([first, second]);
@@ -266,7 +267,7 @@ export function tests() {
             assert.deepEqual(it.next().value, ["b", 3]);
             assert.equal(it.next().done, true);
         },
-        "adding occluded key doesn't emit add": assert => {
+        "adding occluded key doesn't emit add": (assert): void => {
             const first = new ObservableMap();
             const second = new ObservableMap();
             const join = new JoinedMap([first, second]);
@@ -278,7 +279,7 @@ export function tests() {
             assert.equal(events[0].key, "a");
             assert.equal(events[0].value, 1);
         },
-        "updating occluded key doesn't emit update": assert => {
+        "updating occluded key doesn't emit update": (assert): void => {
             const first = new ObservableMap();
             const second = new ObservableMap();
             const join = new JoinedMap([first, second]);
@@ -288,7 +289,7 @@ export function tests() {
             second.update("a", 3);
             assert.equal(events.length, 0);
         },
-        "removal of occluding key emits add after remove": assert => {
+        "removal of occluding key emits add after remove": (assert): void => {
             const first = new ObservableMap();
             const second = new ObservableMap();
             const join = new JoinedMap([first, second]);
@@ -304,7 +305,7 @@ export function tests() {
             assert.equal(events[1].key, "a");
             assert.equal(events[1].value, 2);
         },
-        "adding occluding key emits remove first": assert => {
+        "adding occluding key emits remove first": (assert): void => {
             const first = new ObservableMap();
             const second = new ObservableMap();
             const join = new JoinedMap([first, second]);
diff --git a/src/observable/map/LogMap.ts b/src/observable/map/LogMap.ts
index 6f3bf676..2a084401 100644
--- a/src/observable/map/LogMap.ts
+++ b/src/observable/map/LogMap.ts
@@ -42,47 +42,48 @@ export class LogMap<K, V> extends BaseObservableMap<K, V> {
         return this._log.log(labelOrValues, logLevel);
     }
 
-    onAdd(key: K, value: V) {
+    onAdd(key: K, value: V): void {
         this.log("add " + JSON.stringify({key, value}));
         this.emitAdd(key, value);
     }
 
-    onRemove(key: K, value: V) {
+    onRemove(key: K, value: V): void {
         this.log("remove " + JSON.stringify({key, value}));
         this.emitRemove(key, value);
     }
 
-    onUpdate(key: K, value: V, params: any) {
+    onUpdate(key: K, value: V, params: any): void {
         this.log("update" + JSON.stringify({key, value, params}));
         this.emitUpdate(key, value, params);
     }
 
-    onSubscribeFirst() {
+    onSubscribeFirst(): void {
         this.log("subscribeFirst");
         this._subscription = this._source.subscribe(this);
         super.onSubscribeFirst();
     }
 
-    onUnsubscribeLast() {
+    onUnsubscribeLast(): void {
         super.onUnsubscribeLast();
         if (this._subscription) this._subscription = this._subscription();
         this.log("unsubscribeLast");
     }
 
-    onReset() {
+    onReset(): void {
         this.log("reset");
         this.emitReset();
     }
 
+    // eslint-disable-next-line @typescript-eslint/explicit-function-return-type
     [Symbol.iterator]() {
         return this._source[Symbol.iterator]();
     }
 
-    get size() {
+    get size(): number {
         return this._source.size;
     }
 
-    get(key: K) {
+    get(key: K): V | undefined{
         return this._source.get(key);
     }
 
diff --git a/src/observable/map/MappedMap.ts b/src/observable/map/MappedMap.ts
index 396802bb..e37e313b 100644
--- a/src/observable/map/MappedMap.ts
+++ b/src/observable/map/MappedMap.ts
@@ -46,28 +46,28 @@ export class MappedMap<K, V> extends BaseObservableMap<K, V> {
         this._config = config<K, V>();
     }
 
-    _emitSpontaneousUpdate(key: K, params: any) {
+    _emitSpontaneousUpdate(key: K, params: any): void {
         const value = this._mappedValues.get(key);
         if (value) {
             this.emitUpdate(key, value, params);
         }
     }
 
-    onAdd(key: K, value: V) {
+    onAdd(key: K, value: V): void {
         const emitSpontaneousUpdate = this._emitSpontaneousUpdate.bind(this, key);
         const mappedValue = this._mapper(value, emitSpontaneousUpdate);
         this._mappedValues.set(key, mappedValue);
         this.emitAdd(key, mappedValue);
     }
 
-    onRemove(key: K/*, _value*/) {
+    onRemove(key: K/*, _value*/): void {
         const mappedValue = this._mappedValues.get(key);
         if (this._mappedValues.delete(key)) {
             if (mappedValue) this.emitRemove(key, mappedValue);
         }
     }
 
-    onUpdate(key: K, value: V, params: any) {
+    onUpdate(key: K, value: V, params: any): void {
         // if an update is emitted while calling source.subscribe() from onSubscribeFirst, ignore it
         if (!this._mappedValues) {
             return;
@@ -80,7 +80,7 @@ export class MappedMap<K, V> extends BaseObservableMap<K, V> {
         }
     }
 
-    onSubscribeFirst() {
+    onSubscribeFirst(): void {
         this._subscription = this._source.subscribe(this);
         for (let [key, value] of this._source) {
             const emitSpontaneousUpdate = this._emitSpontaneousUpdate.bind(this, key);
@@ -90,22 +90,23 @@ export class MappedMap<K, V> extends BaseObservableMap<K, V> {
         super.onSubscribeFirst();
     }
 
-    onUnsubscribeLast() {
+    onUnsubscribeLast(): void {
         super.onUnsubscribeLast();
         if (this._subscription) this._subscription = this._subscription();
         this._mappedValues.clear();
     }
 
-    onReset() {
+    onReset(): void {
         this._mappedValues.clear();
         this.emitReset();
     }
 
+    // eslint-disable-next-line @typescript-eslint/explicit-function-return-type
     [Symbol.iterator]() {
         return this._mappedValues.entries();
     }
 
-    get size() {
+    get size(): number {
         return this._mappedValues.size;
     }
 
diff --git a/src/observable/map/ObservableMap.ts b/src/observable/map/ObservableMap.ts
index 6ce6ea91..c49d31dc 100644
--- a/src/observable/map/ObservableMap.ts
+++ b/src/observable/map/ObservableMap.ts
@@ -117,9 +117,10 @@ export class ObservableMap<K, V> extends BaseObservableMap<K, V> {
     }
 };
 
+// eslint-disable-next-line @typescript-eslint/explicit-function-return-type
 export function tests() {
     return {
-        test_initial_values(assert) {
+        test_initial_values(assert): void {
             const map = new ObservableMap([
                 ["a", 5],
                 ["b", 10]
@@ -129,7 +130,7 @@ export function tests() {
             assert.equal(map.get("b"), 10);
         },
 
-        test_add(assert) {
+        test_add(assert): void {
             let fired = 0;
             const map = new ObservableMap<number, {value: number}>();
             map.subscribe({
@@ -147,7 +148,7 @@ export function tests() {
             assert.equal(fired, 1);
         },
 
-        test_update(assert) {
+        test_update(assert): void {
             let fired = 0;
             const map = new ObservableMap<number, {number: number}>();
             const value = {number: 5};
@@ -168,7 +169,7 @@ export function tests() {
             assert.equal(fired, 1);
         },
 
-        test_update_unknown(assert) {
+        test_update_unknown(assert): void {
             let fired = 0;
             const map = new ObservableMap<number, {number: number}>();
             map.subscribe({
@@ -182,7 +183,7 @@ export function tests() {
             assert.equal(result, false);
         },
 
-        test_set(assert) {
+        test_set(assert): void {
             let add_fired = 0, update_fired = 0;
             const map = new ObservableMap<number, {value: number}>();
             map.subscribe({
@@ -209,7 +210,7 @@ export function tests() {
             assert.equal(update_fired, 1);
         },
 
-        test_remove(assert) {
+        test_remove(assert): void {
             let fired = 0;
             const map = new ObservableMap<number, {value: number}>();
             const value = {value: 5};
@@ -229,7 +230,7 @@ export function tests() {
             assert.equal(fired, 1);
         },
 
-        test_iterate(assert) {
+        test_iterate(assert): void {
             const results: any[] = [];
             const map = new ObservableMap<number, {number: number}>();
             map.add(1, {number: 5});
@@ -243,7 +244,7 @@ export function tests() {
             assert.equal(results.find(([key]) => key === 2)[1].number, 6);
             assert.equal(results.find(([key]) => key === 3)[1].number, 7);
         },
-        test_size(assert) {
+        test_size(assert): void {
             const map = new ObservableMap<number, {number: number}>();
             map.add(1, {number: 5});
             map.add(2, {number: 6});