The callback function in JavaScript is not updating AngularJS unless it is written in shorthand form

Within an angular controller designed for user login functionality, the code snippets below are extracted from an angular-meteor tutorial:

    this.login = function() {
        Meteor.loginWithPassword(this.credentials.email, this.credentials.password, (err) => {
            if (err) {
                this.error = err.reason;
            }
            else {
                $state.go('index');
            }
        });
    };

and:

    this.login = function() {
        Meteor.loginWithPassword(this.credentials.email, this.credentials.password, function(err) {
            if (err) {
                this.error = err.reason;
            }
            else {
                $state.go('index');
            }
        });
    };

The first snippet triggers AngularJS to update the error value after the callback function is executed. However, the second snippet does not trigger an update. The key difference between the two lies in the use of shorthand method declaration in the first one. What could be the underlying reason for this discrepancy?

Answer №1

This is not just a quick way to write code, the first example uses an arrow function instead of a traditional function lambda. Arrow functions handle scope differently compared to regular functions.

Arrow functions inherit their parent's scope, eliminating the need to explicitly bind 'this' as shown in this example.

When using a traditional function lambda, you are required to use the 'bind' method to set the context of 'this':

this.login = function() {
        Meteor.loginWithPassword(this.credentials.email, this.credentials.password, function(err) {
            if (err) {
                this.error = err.reason;
            }
            else {
                $state.go('index');
            }
        }.bind(this));
    };

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