Node.js This Binding

Arrow functions do not bind their own this and instead inherit it from the surrounding scope. This makes them useful for callbacks but unsuitable for object methods.

Arrow functions use lexical this from the outer scope.
Not suitable for object methods because this won’t refer to the object.
ES6 method shorthand should be used for defining methods.
Ideal for callbacks like forEach where outer this access is needed.

Filename: index.js

javascript

// 'This' in Arrow function
const eventOne = {
    name: 'Birthday Party',
    guestList: ['Ginny', 'Nicol'],
    printGuestList() {
        console.log('Guest list for ' + this.name);
        this.guestList.forEach((guest) => {
            console.log(guest + ' is attending ' + this.name)
        });
    }
}

// 'This' in normal function
const eventTwo = {
    name: 'Birthday Party',
    guestList: ['Ginny', 'Nicol'],
    printGuestList() {
        console.log('Guest list for ' + this.name);
        this.guestList.forEach(function (guest) {
            console.log(guest + ' is attending ' + this.name)
        });
    }
}

eventOne.printGuestList();
console.log('---------------------');
eventTwo.printGuestList();

Run index.js file using the following command:

node index.js

Arrow functions use lexical this, so they access the object’s this correctly.
In eventOne, this.name works because the arrow function inherits this.
Normal functions have their own this, so context is lost inside forEach.
In eventTwo, this.nanome becomes undefined inside the callback.

So this is how 'this' binding works on arrow functions and normal functions.

Explore