Promise synchronous settle

promise-settle.js

const call = Function.call.bind(Function.call)
// `onSettled` is just `onSettled(value, isSuccess)`.
Promise.hookIntoSettlement = (thenable, onSettled) => {
    function settle(value) {
        let settled = false
        let then

        function fail(e) {
            if (!settled) {
                settled = true
                onSettled(e, false)
            }
        }

        function pass(v) {
            if (!settled) {
                settled = true
                settle(v)
            }
        }

        if (value != null) {
            try {
                then = value.then
                if (then != null) {
                    call(then, value, pass, fail)
                    return
                }
            } catch (e) {
                fail(e)
                return
            }
        }
        onSettled(value, true)
    }
    settle(thenable)
}