Learning how to use arrow functions with the `subscribe` function in

Question

Learning how to use arrow functions with the `subscribe` function in

Can someone help clarify the use of arrow functions in TypeScript with an example from Angular 2's Observable subscribe method? Here's my question:

I have code that is functional:

 this.readdataservice.getPost().subscribe(
            posts => { this.posts = posts; }
        );

But would it work the same way if I try using this approach? It doesn't seem to work.

this.readdataservice.getPost().subscribe(
            function (posts) {
                this.posts = posts;
            }

        );

javascript angular typescript arrow-functions

Answer 1

Answer №1

Arrow functions are unique because they are anonymous and do not bind their own this. As a result, the this keyword refers to the current context.
In contrast, normal functions bind the this keyword to the caller if it is not explicitly bound.

In the following example:

    this.readdataservice.getPost().subscribe(
        posts => { this.posts = posts; }
    );

Can also be written as:

    var self = this;
    this.readdataservice.getPost().subscribe(
        function(posts) { self.posts = posts; }
    );

Alternatively, you can use the following approach:

    this.readdataservice.getPost().subscribe(
        function(posts) { this.posts = posts; }.bind(this)
    );

Answer 2

Arrow functions are unique because they are anonymous and do not bind their own this. As a result, the this keyword refers to the current context.
In contrast, normal functions bind the this keyword to the caller if it is not explicitly bound.

In the following example:

    this.readdataservice.getPost().subscribe(
        posts => { this.posts = posts; }
    );

Can also be written as:

    var self = this;
    this.readdataservice.getPost().subscribe(
        function(posts) { self.posts = posts; }
    );

Alternatively, you can use the following approach:

    this.readdataservice.getPost().subscribe(
        function(posts) { this.posts = posts; }.bind(this)
    );

Answer 3

Answer №2

JavaScript typically runs functions within the scope of the caller, meaning that when a function is passed around and called elsewhere, the reference to this will point back to the original caller. In your scenario, you are passing a function to an observable using the subscribe(...) method, which then executes the function when an event is emitted.

However, if you use arrow functions, the reference to this remains fixed to where it was defined in the code.

Another approach is to utilize .bind(this) to explicitly instruct JavaScript to maintain the reference to this at the current class instance.

    this.readdataservice.getPost().subscribe(
        function (posts) {
            this.posts = posts;
        }.bind(this)

    );

For more information, check out https://developer.mozilla.org/de/docs/Web/JavaScript/Reference/Functions/Arrow_functions

Answer 4

JavaScript typically runs functions within the scope of the caller, meaning that when a function is passed around and called elsewhere, the reference to this will point back to the original caller. In your scenario, you are passing a function to an observable using the subscribe(...) method, which then executes the function when an event is emitted.

However, if you use arrow functions, the reference to this remains fixed to where it was defined in the code.

Another approach is to utilize .bind(this) to explicitly instruct JavaScript to maintain the reference to this at the current class instance.

    this.readdataservice.getPost().subscribe(
        function (posts) {
            this.posts = posts;
        }.bind(this)

    );

For more information, check out https://developer.mozilla.org/de/docs/Web/JavaScript/Reference/Functions/Arrow_functions

Learning how to use arrow functions with the `subscribe` function in

Answer №1

Answer №2

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