ecmascript-6 – About the relationship between "use strict" and ECMAScript6

Question: Question:

Will what happens only when "use strict" is set in ECMAScript5 continue in ECMAScript6?
-For example, when a function is called, will "the phenomenon that this becomes undefined in strict mode and becomes global this (window in the browser) in non-strict mode" continue?
-If you do not explicitly add "use strict" as usual, will it not be undefined in the non-strict mode?

Answer: Answer:

The Strict Mode distinction continues in ECMAScript 2015 (ES6) / ECMAScript 2016.
Existing behavior cannot be modified for backwards compatibility.

However, where there is no need to consider backward compatibility, it defaults to Strict Mode behavior.
In particular,

Inside the Class definition
Whole code loaded as Modules

is.

Inside the Class definition

class A {
    foo() {
        console.log("ここは Strict Mode です");
    }
}

console.log("ここは Strict Mode ではありません");

function foo() {
    "use strict";
    console.log("ここは Strict Mode です");
}

Whole code loaded as Modules

In the browser, if you load the JavaScript code as type="module" as follows, the code will be treated as a module.

<script type="module" src="foo.js"></script>

All code loaded as a module will be forced into Strict Mode.