javascript, promises, how to access variable this inside a then scope [duplicate]

Question

I want to be able to call a function inside the .then scope, and for that I use the this.foo() manner. But if I do this inside the .then I get an error, since this appears to be lost. What can I do?

In this code, this would be equivalent to have the same output for the object this

console.log(this) one().then(function() {   console.log(this) })  function one() {   var deferred = $q.defer();   deferred.resolve()   return deferred.promise; } 

This neither seems to work

console.log(this) var a = this; one().then(function(a) {   console.log(a) }) 

Answer 1

Your second code example is the right way to go. Because the scope changes in the new function, this changes too, so you're right to make a reference to this outside of the function.

The reason it failed is because the function is using a that you passed into the function rather than the global a you defined outside it.

In other words:

var a = this;  one().then(function () {   console.log(a) }); 

Update: use an arrow function - they borrow the context (this) from their outer scope.

function two() {   console.log('Done'); }  one().then(() => {   this.two(); });  function one() {   return new Promise(res => {     setTimeout(() => res(), 2000);   }); }