JavaScript React Basics (retired) Designing Data Flow Adding Players to the Scoreboard

Gonzalo Muro
Gonzalo Muro
5,281 Points

I dont understand yet what is the .bind(this) function for. Can you explain that to me please?

In the "Handling Events" section of the React Documentation, says the following:

// This binding is necessary to make this work in the callback this.handleClick = this.handleClick.bind(this);

, but why?

Is it because if we don't do that "this" will access only to his own scope (handleClick function) instead of the component scope?

"this" inside a function refers to an object, but which object it refers to depends on the how the function is called.

Consider the following example from "YDKJS"

function foo() {
    console.log( this.bar );
}

var bar = "global";

var obj1 = {
    bar: "obj1",
    foo: foo
};

var obj2 = {
    bar: "obj2"
};

// --------

foo();              // "global"
obj1.foo();         // "obj1"
foo.call( obj2 );   // "obj2"

You use bind() to create bounded methods and by binding this.handleClick to "this" , you make sure that no matter how you call your function the context remains the same.

As per the react documentation, they recommend binding your event handlers in the constructor so they are only bound once for every instance.