Question

61

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

rated 0 times [ 67] [ 6] / answers: 1 / hits: 76205 / 9 Years ago, sun, september 13, 2015, 12:00:00

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)

})

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tayaw

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answered 9 Years ago freddiej · Accepted Answer

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);

  });

}