Doubt with scope js

Question

I know that variable statements are all high for the whole of the scope, but I was left with a little doubt about this, the use of the word 'use Strict' avoids q declare variables like this

a = 10

But why in this situation below it allows to show the value of this in the function even if with the word 'use Strict'.

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

"use strict";
function minhaFuncao() {
  console.log(this); //Deveria ter mostrado undefined
 }
 myFunction();
 foo();

The elevation occurred and would have been like this ?

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

 function minhaFuncao(){
    console.log(this);
 }

'use Strict';

Is it right what I’m thinking ? , or something else happened, thanks in advance

Answer 1

The this is not a variable, is the value corresponding to the execution context of a function. It is always present and cannot be declared.

In your case as the function does not belong to any object or class it has the window as an implementation context.

However you can limit the value this in global functions, or wherever the this would be the window. This has to do with security reasons, to avoid that via the browser console it is possible to change code values.

Look at the examples below:

class Foo {
  constructor() {
    this.name = 'classe';
  }
  foo() {
    console.log(this);
  }
}

new Foo().foo(); // Foo {name: "classe"}

const obj = {
  foo: function() {
    console.log(this); // {foo: ƒ, name: "objeto"}
  },
  name: 'objeto'
}

obj.foo();

function foo() {
  console.log(this === window);
}

foo(); // true

function bar(){
  'use strict';
  console.log(this); // undefined
}

bar();

That is, if the function does not belong to an object or class, it belongs to the object window by default but you can limit global access by using use strict.