javascript - how to do `var self = this` inside es6 class?

Question

I am running the below code in nodejs

this.x = 'global x';
class Point {
    constructor(x) {
        this.x = x;
    }
    toString() {
        return this.x;
    }
}
var obj = new Point(1);
obj.toString();// 1 as expected
var a = obj.toString;// Here I can do something like var a = obj.toString.bind(obj); to get rid of the situation. But I am curious to know how can we write `var self = this`;
a();// TypeError: Cannot read property 'x' of undefined

a(); throws the error.
How can we do like var self = this; as we used to do in es5 to prevent such a situation?

Answer 1

How can we do like var self = this; as we used to do in ES5?

You can do it exactly like you did in ES5 - ES6 is completely backward-compatible after all:

class Point {
    constructor(x) {
        this.x = x;
        var self = this;
        this.toString = function() {
            return self.x;
        };
    }
}

However, that's really not idiomatic ES6 (not talking about const instead of var). You'd rather use an arrow function that has a lexical-scoped this, so that you can avoid this self variable completely:

class Point {
    constructor(x) {
        this.x = x;
        this.toString = () => {
            return this.x;
        };
    }
}

(which could even be shortened to this.toString = () => this.x;)