48 lines
1.3 KiB
JavaScript
48 lines
1.3 KiB
JavaScript
/*
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A somewhat refined Proxy generator that lets you selectively listen to changed
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properties and react accordingly.
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Example:
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const l = listener()
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l.listen("contract", contract => speaker.handle(contract))
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l.contract = new Contract()
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*/
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const registry = new Map()
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const listener = (target={}) => {
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const callbacks = new Map()
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const methods = Object.create(null)
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methods.listen = function(name, fn, {once=false}={}) {
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const callback = once
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? (...args) => { this.forget(name, callback); return fn(...args) }
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: fn
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let set = callbacks.get(name) ?? new Set()
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callbacks.set(name, set)
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set.add(callback)
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return this
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}
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methods.forget = function(name, callback) {
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if (callback) {
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const set = callbacks.get(name)
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if (set) return set.delete(callback)
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} else {
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return callbacks.delete(name)
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}
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}
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let proxy = new Proxy(target, {
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set: (target, prop, value) => {
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if (callbacks.has(null)) callbacks.get(null).forEach(callback => callback(value, target[prop], prop))
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if (callbacks.has(prop)) callbacks.get(prop).forEach(callback => callback(value, target[prop], prop))
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return Reflect.set(target, prop, value)
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},
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get: (target, prop, value) => prop in methods
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? methods[prop]
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: target[prop]
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})
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registry.set(proxy, target)
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return proxy
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}
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listener.raw = proxy => registry.get(proxy)
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export default listener
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