JavaScript field access from anonymous function

Question

how can I access a fiel from within an anonymous function inside a method? like in this example:

class Something {
    constructor (){
        this.gax = “gax”;
    }
    doSomething(){
        (function () {
           console.log(this.gax);
        }());
    }
}
new Something().doSomething();

this will result in an error that "this" is undefined. thank you very much in advance, I could not find an answer in the web after searching for hours. best, lev

Probably relevent: [another SO answer](https://stackoverflow.com/questions/2236747/what-is-the-use-of-the-javascript-bind-method) — Dale, Nov 22 '19 at 15:45
...or possibly [access correct 'this' in a callback](https://stackoverflow.com/questions/20279484/how-to-access-the-correct-this-inside-a-callback) ...or about a half-dozen others, incl the one mentioned by @Dale. — Jared Smith, Nov 22 '19 at 15:49

Tyler Roper · Accepted Answer · 2019-11-22T15:47:28.157

In your anonymous function, this is bound to the function; it no longer refers to the class.

Use an arrow function instead, which doesn't have it's own this binding.

class Something {
    constructor (){
        this.gax = "gax";
    }
    doSomething(){
        (() => {
           console.log(this.gax);
        })();
    }
}
new Something().doSomething();

Alternatively, you could use something like .call(), .apply(), or .bind():

class Something {
    constructor (){
        this.gax = "gax";
    }
    doSomething(){
        (function() {
           console.log(this.gax);
        }).call(this);
    }
}
new Something().doSomething();

score 0 · Answer 2 · answered Nov 22 '19 at 15:47

class Something {
    constructor (){
        this.gax = "gax";
    }
    doSomething(){
        (function () {
           console.log(this.gax);
        }).apply(this);
    }
}
new Something().doSomething();

You can use apply method. The apply() method calls a function with a given this value

JavaScript field access from anonymous function

2 Answers2