CommonJS vs. ES Modules: this Behavior with call(null) and call(undefined)

Question

I saved the following code as index.cjs so that node considers it as a CommonJS module.

console.log(this);
function getThis() {
  console.log("this", this);
}
getThis.call(null); 
getThis.call(undefined);

I ran the above file using the command $ node index.cjs

I am using node v18.17.0. I am getting the output as - empty object({}), global object, global object

When I run the above file with .mjs extension, i.e. when node treats it as an ES module, I am getting the output undefined, null, undefined

**Why there is a difference in the output? **

While trying to find the answer, I came across the following points but they do not fully justify the output which I am getting.

1. Node.js CommonJS modules are wrapped in a function and executed with the this value set to module.exports. This explains why empty object is printed in CJS at top-level.
2. this substitution does not takes place in strict mode and modules by default runs in strict mode. When running the file as CJS module, it seems this substituition takes place. Hence it prints gloal object even when I call the function by setting its context explicitly to null and undefined.

Furthermore, when I add the statement use strict in index.cjs, the output is - {} this null this undefined

• Jaromanda X: ES module implies "use strict" - put that at the top of the file and you'll see a difference in commonJS ... the fact that this is {} in commonJS is probably how commonJS is specified to work
• evolutionxbox: In addition to what @JaromandaX has already said, you can even see this behaviour replicated directly in your browser's console.
• Arman Lalani: @JaromandaX So, strict mode is implied in ES modules, and in CommonJS modules, it is not. Is that correct?