Differences Between 'this' and 'self' in Classes

I am currently working with ES6 Classes and I'm struggling to grasp why I am able to access the this variable within one of the methods.

//CODE

class Form{ 
    constructor(){
        var self = this;
    }   

    assemble(){
        log(self);
    }
}

//INVOCATION

var form = new Form();
form.assemble();

//RESULT

window object (not a reference to the class object)

Answer №1

this is not a variable. It functions more like a concealed argument in functions.

In the given example, you cannot access self because it is a local variable confined within the constructor and therefore unavailable to your assemble method.

For this particular scenario, you actually do not require self at all; simply utilize this:

class Form {
    assemble(){
        log(this);             // ***
    }
}
var form = new Form();
form.assemble();

If you were passing form.assemble into something where the correct usage of this was not guaranteed, you could define assemble as an instance function member by defining it within the constructor; thus closing over self. Nonetheless, in ES2015 and beyond, there is no need for self; instead, use an arrow function which closes over this:

class Form {
    constructor(){
        var self = this;
        this.assemble = () => {
            log(this);
        };
    }   
}
var form = new Form();
form.assemble();          // Functions correctly
var f = form.assemble;
f();                      // Also works fine

However, chances are high that this additional step is unnecessary.

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