Promise.newCapability prollyfill

promise-newcapability.js

Promise.newCapability = Promise.newCapability || (() => {
    const data = new WeakMap()
    const getData = data.get.bind(data)
    const setData = data.set.bind(data)
    const objectCreate = Object.create

    function invokeResolver(inst, index, value) {
        const data = getData(inst)
        if (data == null) throw new TypeError()
        const func = data[index]
        if (func != null) {
            data[1] = data[2] = void 0
            func(value)
        }
    }

    class Capability {
        constructor(data) {
            setData(this, data)
        }

        get promise() {
            const data = getData(inst)
            if (data == null) throw new TypeError()
            return data[0]
        }

        resolve(value) {
            invokeResolver(this, 1, value)
        }

        reject(value) {
            invokeResolver(this, 2, value)
        }
    }

    delete Capability.prototype.constructor

    return {newCapability() {
        const data = [void 0, void 0, void 0]
        data[0] = new this((resolve, reject) => {
            data[1] = resolve
            data[2] = reject
        })
        return new Capability(data)
    }}.newCapability
})()