How does the explicit binding using call() works in Javascript?

Question

If null or nothing is passed in call(), would it be considered as implicit binding? What should be the output of the following code? Isn't it should be 2? I am getting 'undefined'.

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

var a = 2;

foo.call( null ); // 2

From mdn; "If the method is a function in non-strict mode, null and undefined will be replaced with the global object" — IAmDranged
– IAmDranged, Commented Apr 6, 2021 at 18:46

yeputons · Accepted Answer · 2021-04-06 18:37:41Z

4

It is an implicit binding, you can check that with console.log(this);. It prints the global object. So, when run in my browser, your code prints 2.

However, such var a = 2; statement works differently in Node.js: it does not create a property of the global object. So this.a tries to access a non-existing member which results in undefined.

answered Apr 6, 2021 at 18:37

yeputons

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1 Comment

Emile Bergeron Over a year ago

Additional info: the interactive Node console returns 2 as well (non-strict code) as it creates a global object.

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