将一个js文件包含在另一个文件中的正确方法是什么？

Question

The following JavaScript code works:

let Color = require('color');

class Example {
    its_not_easy_being_green() {
        return Color('green');
    }
}

test('It is not easy being green', () => {
    expect(new Example().its_not_easy_being_green()).toBeDefined();
})

and npx jest gets me a greenbar.

$ npx jest
 PASS  test/example.spec.js
  ✓ It is not easy being green (2 ms)

Test Suites: 1 passed, 1 total
Tests:       1 passed, 1 total
Snapshots:   0 total
Time:        0.351 s, estimated 1 s
Ran all test suites.

However, any time I try to separate the class from the test I get various errors:

The most common is one about not being permitted to use import outside a module.

Or that Example is not a constructor.

What I am trying to do is move everything that isn't the three line test out of the JavaScript file that I've posted above.

If this were Java, I'd move that stuff into a separate .java file and then import that file in my test.

If this were C there would be a linker and #include involved.

What I've tried is to create an Example.js file:

let Color = require('color');

class Example {
    its_not_easy_being_green() {
        return Color('green');
    }
}

and then require it in the test:

let Example = require('Example.js')

test('It is not easy being green', () => {
    expect(new Example().its_not_easy_being_green()).toBeDefined();
})

But that gets me a complaint about Example not being a constructor, which, I suppose is true. It is a class, which presumably has a pretty inert default constructor of some kind.

I've also tried replacing the require with an import :

import('Example.js')

test('It is not easy being green', () => {
    expect(new Example().its_not_easy_being_green()).toBeDefined();
})

But that gets complaints about not being permitted to use import outside a module.

Is it possible to separate the jest test from the code being tested in JavaScript?

Answer 1

There is no #include in Javascript - it uses a module system instead where you export things you want to share.

It is best to learn the tools the language offers rather than trying to force it to do something the way a different language does things.

Also, note there are two types of modules in nodejs, CommonJS modules that use require() and module.exports and ESM modules that use import and export . Your project appears to be set up for CommonJS so that's what you would use unless you want to configure the project to be an ESM module project and then use the ESM rules for importing and exporting.

For a CommonJS project:

const Color = require('color');

class Example {
    its_not_easy_being_green() {
        return Color('green');
    }
}

module.exports.Example = Example;

Then, in your main file:

const { Example } = require('./Example.js')

test('It is not easy being green', () => {
    expect(new Example().its_not_easy_being_green()).toBeDefined();
});