Interview question: javascript implement Promise.all

promiseAll.js

var promiseAll = (ps) => {
    return new Promise((resolve) => {
        var c = ps.length
        for (var p of ps) {
            p.then(() => {
                c--
                if (c == 0) {
                    resolve()
                }
            })
        }
    })
}
describe("promiseAll", () => {
    it("1", () => {
        var ps = []
        ps.push(new Promise((resolve) => {
            setTimeout(() => {
                console.log("p1")
                resolve()
            }, 100)
        }))
        ps.push(new Promise((resolve) => {
            setTimeout(() => {
                console.log("p2")
                resolve()
            }, 200)
        }))
        return promiseAll(ps).then(() => {
            console.log("finish all")
        })
    })
})

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