17. The scope chain #

Created Wednesday 2 March 2022

• [ ] in vault

Consider this code:

function b() {
	console.log(myVar);
}

function a() {
	let myVar = 2;
	b();
}

let myVar = 1;
a(); // prints 1

This code snipper indicates that JavaScript looks for variables not in the current execution context, in the next outer lexical environment and so on. This is the scope chain traversal.

Note that execution context (activation record) and lexical environment (scope) are two different things. This is the reason the lexical environment does not always behave like a stack, like here.

Of course, one should not write code like this, and keep the declarations above the use.

However, we can change the lexical environment for b. For example:

function a() {
	function b() {
		console.log(myVar);
	}
	let myVar = 2;
	b()
}

a();