Do you know what will be the output of this code? function f() { y = 10; } f(); console.log(y);

What happens when you assign a variable without declaring it?

Do you know what will be the output of this code?

JavaScript

function f() {
  y = 10;
}

f();
console.log(y);

Show answer and explanation

The answer is 10.

Without var, let or const, the assignment creates a property on the global object. That’s an accidental global.

In strict mode (and in modules and classes) the same code throws ReferenceError: y is not defined.