javascript: use strict is unnecessary inside of modules

Question

tsling raise an error:

Line 1: 'use strict' is unnecessary inside of modules (strict)

this is my code

"use strict";

function Foo() {}

Foo.prototype.sayHello= function () {
    console.log("hello!");
}

if (typeof module !== 'undefined' && typeof module.exports !== 'undefined') {
    module.exports = { 
        Foo: Foo
    };
}

how fix this error?

Side note

my code is used both module and vanilla javascript. I want use "strict mode" only for vanilla javascript.

maybe i can use

if (typeof module !== 'undefined') {
    "use strict";
}

for enabling strict mode only for vanilla javascript?

Answer 1

Remove 'use strict'. As the error mentions, it's unnecessary. Modules are expected to execute in strict mode. Compilers will add it for you when you export the module into a script for non-module consumption (i.e. UMD/CJS). See --alwaysStrict option for TS.

Answer 2

ES6 modules are always in strict mode.