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transmuter-store.js
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transmuter-store.js
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/**
* Store container object
*
* @author Iain van der Wiel
* @param {String} name Name of store
* @param {Object} target Target object containing the state to watch
* @param {Element} context Element or object to dispatch events on
* @returns {TransmuterStore} Store object containing name, context and state Proxy
*/
class TransmuterStore {
constructor(name, target, context = window) {
this.name = name;
this.context = context;
this.state = new Proxy(target, TransmuterStore.createHandler(this));
}
}
TransmuterStore.createHandler = store => ['set', 'deleteProperty', 'apply', 'defineProperty'].reduce((handler, method) => {
handler[method] = (state, prop, value) => {
const success = Reflect[method](state, prop, value);
if (success) {
// Setup custom event
const event = new CustomEvent(`${store.name}:${prop}`, {
detail: {
prop,
value,
oldValue: state[prop],
state: store.state,
},
});
// Dispatch name:prop event on context
store.context.dispatchEvent(event);
}
return success;
};
return handler;
}, {});
/**
* Store listener
* @param {TransmuterStore} store Store object to listen to
* @param {String|Array} props Prop(s) of the store to watch
* @param {Function} handler Handler function that's called when a property changes
*/
const listen = ({ name, context }, props, handler) => {
// Concat props in new array. This allows strings and arrays of props to listen to.
let propsToListen = [].concat(props);
// Listener callback that destructures values from event.detail
const listener = ({
detail: {
prop, value, oldValue, state,
},
}) => handler(prop, value, oldValue, state);
// Listen to single prop
const listenToProp = prop => context.addEventListener(`${name}:${prop}`, listener);
// Stop listening to single prop
const stopListeningToProp = prop => context.removeEventListener(`${name}:${prop}`, listener);
// Apply listener to watched props
const start = () => propsToListen.forEach(listenToProp);
// Remove listener to watched props
const stop = () => propsToListen.forEach(stopListeningToProp);
// Add prop to listen to
const addProp = (propToAdd) => {
listenToProp(propToAdd);
propsToListen = [...propsToListen, propToAdd];
};
// Remove listened prop
const removeProp = (propToRemove) => {
stopListeningToProp(propToRemove);
propsToListen = propsToListen.filter(prop => prop !== propToRemove);
};
// Kickstart the listening
start();
// Return listener API
return {
start,
stop,
addProp,
removeProp,
};
};
export { TransmuterStore, listen };