SOURCE

function mockPromise(resolver) {
    // states
    // 0: pending
    // 1: resolving
    // 2: rejecting
    // 3: resolved
    // 4: rejected
    var self = this,
    state = 0;

    try {
        if (typeof resolver === 'function') resolver(self.resovle, self.reject)
    } catch (e) {
        self.reject(e);
    }
}

var a = new mockPromise();