returning ES6 promise from constructor - binding this

Question

I want to do

X.prototype.f = function() {
    return new Promise(
        function(resolve, reject) {
           if (this.f1()==0) resolve();
           ...

however this (that is the X instance) is not defined inside the promise constructor. I understand I need to bind this somehow but not sure how to proceed ?

Answer 1

As you're using es6, why aren't you using es6?

X.prototype.f = function() {
    return new Promise((resolve, reject) => {
       if (this.f1()==0) resolve();
    });
}

Answer 2

You can assign this to another variable inside the function

X.prototype.f = function() {
    var self = this;
    return new Promise(
        function(resolve, reject) {
           if (self.f1()==0) resolve();
           ...