js/listener.js

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/*
A somewhat refined Proxy generator that lets you selectively listen to changed
properties and react accordingly.
Example:
const l = listener()
l.listen("contract", contract => speaker.handle(contract))
l.contract = new Contract()
*/
export default (target={}) => {
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let callbacks = new Map()
function listen(prop, callback) {
if ("object" == typeof prop && "forEach" in prop) {
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prop.forEach(prop => this.listen(prop, callback))
} else if (callback) {
let list = callbacks.get(prop)
if (!list) callbacks.set(prop, list=[])
list.push(callback)
} else {
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callbacks.delete(prop)
}
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}
let proxy = new Proxy(target, {
set: (target, prop, value) => {
console.log(callbacks)
if (callbacks.has("*")) callbacks.get("*").forEach(callback => callback(value, prop))
if (callbacks.has(prop)) callbacks.get(prop).forEach(callback => callback(value, prop))
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return Reflect.set(target, prop, value)
},
get: (target, prop, value) => {
if (prop == "listen")
return listen
else
return Reflect.get(target, prop)
}
})
return proxy
}