mastodon/app/javascript/mastodon/initial_state.js

const element = document.getElementById('initial-state');
const initialState = element && JSON.parse(element.textContent);

const getMeta = (prop) => initialState && initialState.meta && initialState.meta[prop];

export const reduceMotion = getMeta('reduce_motion');
export const autoPlayGif = getMeta('auto_play_gif');

export default initialState;