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Trying to understand how to import web-assembly package via webpack

I'm on webpack#4.43.0 and am trying to use this web assembly library https://github.com/vislyhq/stretch As per docs I am importing some classes from it i.e.
import { Allocator, Node } from 'stretch-layout';
class Base {
public layoutNode;
public constructor() {
this.layoutNode = new Node(allocator, {});
}
}
However when I am trying to build it with webpack (not using any loaders and I have .wasm in my resolve.extensions webpack config) I am getting following error
WebAssembly module is included in initial chunk. This is not allowed,
because WebAssembly download and compilation must happen asynchronous.
Add an async splitpoint (i. e. import()) somewhere between your
entrypoint and the WebAssembly module:
To my understanding I need to use import() for this module, but how do I make these imports available to my class? Application will fail since we need to await that import? If I do something like this I get an error saying that Allocator and Node are not constructors.
let Allocator: any = null;
let Node: any = null;
import('stretch-layout').then(module => {
Allocator = module.Allocator;
Node = module.Node;
});

I was able to solve this using latest beta of webpack 5, by adding following experimental flags to config
experiments: {
asyncWebAssembly: true,
importAsync: true
}
this way you don't have to worry about any async import() statements at all

Vue: How to build bundle for Nuxt with vue-cli-service?

A user tries to use my package for nuxt.js, but gets the error: document is not defined.
I found the first issue. When I build the bundle with "build-bundle": "vue-cli-service build --target lib --name index ./src/index.js",
vue-style-loader is being used. This, however, results in the error for using nuxt projects. This part is failing:
function addStyle (obj /* StyleObjectPart */) {
var update, remove
var styleElement = document.querySelector('style[' + ssrIdKey + '~="' + obj.id + '"]')
Document is not defined since we are using server rendering. But the question is how can I build up my package so that I can use it with nuxt?
I need:
index.common.js
index.umd.js
index.umd.min.js

This is due to the server-side rendering. If you need to specify that you want to import a resource only on the client-side, you need to use the process.client variable.
For example, in your .vue file:
if (process.client) {
require('external_library')
// do something
}
The above is the fundamental solution to document is not defined.
I checked some information and found that, this problem is not caused by your package. In fact, the problem lies on the cache-loader package in the user’s nuxt project.
For some reason cache-loader incorrectly determined the current environment as browser and not node so that vue-style-loader is confused and used client implementation instead.
So try to let users add the following configuration to the nuxt.config.js file to disable stylesheet caches on server-side:
build: {
...
cache: true,
extend(config, { isServer, isDev, isClient }) {
...
if (isServer) {
for (const rules of config.module.rules.filter(({ test }) =>
/\.((c|le|sa|sc)ss|styl.*)/.test(test.toString())
)) {
for (const rule of rules.oneOf || []) {
rule.use = rule.use.filter(
({ loader }) => loader !== 'cache-loader'
)
}
}
}
...
}
...
}

I found a solution but it is not using the vue-cli service. Instead, the files are compiled by rollup. I found using the cli service much easier. The only problem with the cli service is it will adjust the "flow" of your repo. However, you can modify the rollup.config.js to amend the folder structure.
The problem with rollup is that it isn't webpack. Therefore, all components using a webpack configuration need to be adjusted or rollup.config.js needs to be amended to include the additional functionality

babel generated code breaking istanbul coverage

I'm using babel to enable ES6 imports in a node project. Also using mocha for testing, and istanbul for coverage. I end up with less than full coverage because babel generates code something like the following:
'use strict';
Object.defineProperty(exports, "__esModule", {
value: true
});
var _promise = require('babel-runtime/core-js/promise');
var _promise2 = _interopRequireDefault(_promise);
var _koa = require('koa');
var _koa2 = _interopRequireDefault(_koa);
function _interopRequireDefault(obj) { return obj && obj.__esModule ? obj : { default: obj }; }
Specifically, the generated function _interopRequireDefault is copied into every code file, and the branches are not necessarily always executed, which skews the branch coverage number emitted for istanbul. Is there any way around this issue?

If you're using gulp, I have a gist with a gulpfile here that sets up the necessary hooks and filters. The relevant chunk is to load isparta, hook require, and let the tests run:
gulp.task('test:cover', (cb) => {
gulp.src('src/main/**/*.js')
.pipe(istanbul({
instrumenter: require('isparta').Instrumenter,
includeUntested: true
}))
.pipe(babel())
.pipe(gulp.dest('target/cover'))
.pipe(istanbul.hookRequire())
.on('finish', cb);
});
gulp.task('test:mocha', (cb) => {
gulp.src('target/test/**/Test*')
.pipe(mocha())
.pipe(istanbul.writeReports())
.on('end', cb);
});
gulp.task('test', (cb) => {
return runSequence('test:cover', 'test:mocha', cb);
});
The only frustrating part is that your tests must use the covered code:
import {
LinearInterpolator,
CosineInterpolator
} from '../../cover/random/Interpolators';
I haven't found a way to work around that yet without also covering the test scripts and skewing coverage, although you should be able to do that by merging streams:
gulp.task('test:cover', (cb) => {
const src = gulp.src('src/main/**/*.js')
.pipe(istanbul({
instrumenter: require('isparta').Instrumenter,
includeUntested: true
}));
const test = gulp.src('src/test/**/*.js');
merge(src, test)
.pipe(babel())
.pipe(gulp.dest('target/cover'))
.pipe(istanbul.hookRequire())
.on('finish', cb);
});

You need to combine it with isparta - https://github.com/douglasduteil/isparta - to get the coverage working correctly. I warn you its a bit trial and error at the moment! My npm script looks like -
"coverage": "node_modules/.bin/babel-node node_modules/.bin/isparta cover --include-all-sources --report html node_modules/.bin/_mocha -- --reporter $npm_package_config_bdd_reporter",

We've run into this and I finally got fed up and looked into what causes this line. It turns out that every time to use an import like:
import chai from 'chai';
this babel fill gets added to allow sane interaction with older export styles. The trouble is that none of the common libraries exhibit the "true" branch of the ternary. I build the following file coverInterrop.js that artificially trips the first branch using old-school exports:
module.exports = {
__esModule: true
};
and I include in any file where I want to use an undestructured import:
// eslint-disable-next-line no-unused-vars
import coverInterrop from 'coverInterrop';
Note that it has to assign to a variable to trip the coverage and good eslint rules won't like that

How can I mock Webpack's require.context in Jest?

Suppose I have the following module:
var modulesReq = require.context('.', false, /\.js$/);
modulesReq.keys().forEach(function(module) {
modulesReq(module);
});
Jest complains because it doesn't know about require.context:
FAIL /foo/bar.spec.js (0s)
● Runtime Error
- TypeError: require.context is not a function
How can I mock it? I tried using setupTestFrameworkScriptFile Jest configuration but the tests can't see any changes that I've made in require.

I had the same problem, then I've made a 'solution'.
I'm pretty sure that this is not the best choice. I ended up stopping using it, by the points answered here:
https://github.com/facebookincubator/create-react-app/issues/517
https://github.com/facebook/jest/issues/2298
But if you really need it, you should include the polyfill below in every file that you call it (not on the tests file itself, because the require will be no global overridden in a Node environment).
// This condition actually should detect if it's an Node environment
if (typeof require.context === 'undefined') {
const fs = require('fs');
const path = require('path');
require.context = (base = '.', scanSubDirectories = false, regularExpression = /\.js$/) => {
const files = {};
function readDirectory(directory) {
fs.readdirSync(directory).forEach((file) => {
const fullPath = path.resolve(directory, file);
if (fs.statSync(fullPath).isDirectory()) {
if (scanSubDirectories) readDirectory(fullPath);
return;
}
if (!regularExpression.test(fullPath)) return;
files[fullPath] = true;
});
}
readDirectory(path.resolve(__dirname, base));
function Module(file) {
return require(file);
}
Module.keys = () => Object.keys(files);
return Module;
};
}
With this function, you don't need to change any require.context call, it will execute with the same behavior as it would (if it's on webpack it will just use the original implementation, and if it's inside Jest execution, with the polyfill function).

After spending some hours trying each of the answers above. I would like to contribute.
Adding babel-plugin-transform-require-context plugin to .babelrc for test env fixed all the issues.
Install - babel-plugin-transform-require-context here https://www.npmjs.com/package/babel-plugin-transform-require-context (available with yarn too)
Now add plugin to .babelrc
{
"env": {
"test": {
"plugins": ["transform-require-context"]
}
}
}
It will simply transform require-context for test env into dummy fn calls so that code can run safely.

If you are using Babel, look at babel-plugin-require-context-hook. Configuration instructions for Storybook are available at Storyshots | Configure Jest to work with Webpack's require.context(), but they are not Storyshots/Storybook specific.
To summarise:
Install the plugin.
yarn add babel-plugin-require-context-hook --dev
Create a file .jest/register-context.js with the following contents:
import registerRequireContextHook from 'babel-plugin-require-context-hook/register';
registerRequireContextHook();
Configure Jest (the file depends on where you are storing your Jest configuration, e.g. package.json):
setupFiles: ['<rootDir>/.jest/register-context.js']
Add the plugin to .babelrc
{
"presets": ["..."],
"plugins": ["..."],
"env": {
"test": {
"plugins": ["require-context-hook"]
}
}
}
Alternatively, add it to babel.config.js:
module.exports = function(api) {
api.cache(true)
const presets = [...]
const plugins = [...]
if (process.env.NODE_ENV === "test") {
plugins.push("require-context-hook")
}
return {
presets,
plugins
}
}
It may be worth noting that using babel.config.js rather than .babelrc may cause issues. For example, I found that when I defined the require-context-hook plugin in babel.config.js:
Jest 22 didn't pick it up;
Jest 23 picked it up; but
jest --coverage didn't pick it up (perhaps Istanbul isn't up to speed with Babel 7?).
In all cases, a .babelrc configuration was fine.
Remarks on Edmundo Rodrigues's answer
This babel-plugin-require-context-hook plugin uses code that is similar to Edmundo Rodrigues's answer here. Props to Edmundo! Because the plugin is implemented as a Babel plugin, it avoids static analysis issues. e.g. With Edmundo's solution, Webpack warns:
Critical dependency: require function is used in a way in which dependencies cannot be statically extracted
Despite the warnings, Edmundo's solution is the most robust because it doesn't depend on Babel.

Extract the call to a separate module:
// src/js/lib/bundle-loader.js
/* istanbul ignore next */
module.exports = require.context('bundle-loader?lazy!../components/', false, /.*\.vue$/)
Use the new module in the module where you extracted it from:
// src/js/lib/loader.js
const loadModule = require('lib/bundle-loader')
Create a mock for the newly created bundle-loader module:
// test/unit/specs/__mocks__/lib/bundle-loader.js
export default () => () => 'foobar'
Use the mock in your test:
// test/unit/specs/lib/loader.spec.js
jest.mock('lib/bundle-loader')
import Loader from 'lib/loader'
describe('lib/loader', () => {
describe('Loader', () => {
it('should load', () => {
const loader = new Loader('[data-module]')
expect(loader).toBeInstanceOf(Loader)
})
})
})

Alrighty! I had major issues with this and managed to come to a solution that worked for me by using a combination of other answers and the Docs. (Took me a good day though)
For anyone else who is struggling:
Create a file called bundle-loader.js and add something like:
module.exports = {
importFiles: () => {
const r = require.context(<your_path_to_your_files>)
<your_processing>
return <your_processed_files>
}
}
In your code import like:
import bundleLoader from '<your_relative_Path>/bundle-loader'
Use like
let <your_var_name> = bundleLoader.importFiles()
In your test file right underneath other imports:
jest.mock('../../utils/bundle-loader', () => ({
importFiles: () => {
return <this_will_be_what_you_recieve_in_the_test_from_import_files>
}
}))

Installing
babel-plugin-transform-require-context
package and adding the plugin in the .babelrc resolved the issue for me.
Refer to the documentation here:
https://www.npmjs.com/package/babel-plugin-transform-require-context

The easiest and fastest way to solve this problem will be to install require-context.macro
npm install --save-dev require-context.macro
then just replace:
var modulesReq = require.context('.', false, /\.js$/);
with:
var modulesReq = requireContext('.', false, /\.js$/);
Thats it, you should be good to go!
Cheers and good luck!

Implementation problems not mentioned:
Jest prevents out-of-scope variables in mock, like __dirname.
Create React App limits Babel and Jest customization. You need to use src/setupTests.js which is run before every test.
fs is not supported in the browser. You will need something like browserFS. Now your app has file system support, just for dev.
Potential race condition. Export after this import. One of your require.context imports includes that export. I'm sure require takes care of this, but now we are adding a lot of fs work on top of it.
Type checking.
Either #4 or #5 created undefined errors. Type out the imports, no more errors. No more concerns about what can or can't be imported and where.
Motivation for all this? Extensibility. Keeping future modifications limited to one new file. Publishing separate modules is a better approach.
If there's an easier way to import, node would do it. Also this smacks of premature optimization. You end up scrapping everything anyways because you're now using an industry leading platform or utility.

If you're using Jest with test-utils in Vue.
Install these packages:
#vue/cli-plugin-babel
and
babel-plugin-transform-require-context
Then define babel.config.js at the root of the project with this configuration:
module.exports = function(api) {
api.cache(true);
const presets = [
'#vue/cli-plugin-babel/preset'
];
const plugins = [];
if (process.env.NODE_ENV === 'test') {
plugins.push('transform-require-context');
}
return {
presets,
plugins
};
};
This will check if the current process is initiated by Jest and if so, it mocks all the require.context calls.

I faced the same issue with an ejected create-react-app project
and no one from the answers above helped me...
My solution were to copy to config/babelTransform.js the follwoing:
module.exports = babelJest.createTransformer({
presets: [
[
require.resolve('babel-preset-react-app'),
{
runtime: hasJsxRuntime ? 'automatic' : 'classic',
},
],
],
plugins:["transform-require-context"],
babelrc: false,
configFile: false,
});

Simpleset Solution for this
Just Do
var modulesReq = require.context && require.context('.', false, /\.js$/);
if(modulesReq) {
modulesReq.keys().forEach(function(module) {
modulesReq(module);
});
}
So Here I have added extra check if require.context is defined then only execute By Doing this jest will no longer complain

How to properly require modules from mocha.opts file

I'm using the expect.js library with my mocha unit tests. Currently, I'm requiring the library on the first line of each file, like this:
var expect = require('expect.js');
describe('something', function () {
it('should pass', function () {
expect(true).to.be(true); // works
});
});
If possible, I'd like to remove the boilerplate require code from the first line of each file, and have my unit tests magically know about expect. I thought I might be able to do this using the mocha.opts file:
--require ./node_modules/expect.js/index.js
But now I get the following error when running my test:
ReferenceError: expect is not defined
This seems to make sense - how can it know that the reference to expect in my tests refers to what is exported by the expect.js library?
The expect library is definitely getting loaded, as if I change the path to something non-existent then mocha says:
"Error: Cannot find module './does-not-exist.js'"
Is there any way to accomplish what I want? I'm running my tests from a gulp task if perhaps that could help.

You are requiring the module properly but as you figured out, the symbols that the module export won't automatically find themselves into the global space. You can remedy this with your own helper module.
Create test/helper.js:
var expect = require("expect.js")
global.expect = expect;
and set your test/mocha.opts to:
--require test/helper

While Louis's answer is spot on, in the end I solved this with a different approach by using karma and the karma-chai plugin:
Install:
npm install karma-chai --save-dev
Configure:
karma.set({
frameworks: ['mocha', 'chai']
// ...
});
Use:
describe('something', function () {
it('should pass', function () {
expect(true).to.be(true); // works
});
});

Thanks to Louis answer and a bit of fiddling around I sorted out my test environment references using mocha.opts. Here is the complete setup.
My project is a legacy JavaScript application with a lot of "plain" js files which I wish to reference both in an html file using script tags and using require for unit testing with mocha.
I am not certain that this is good practice but I am used to Mocha for unit testing in node project and was eager to use the same tool with minimal adaptation.
I found that exporting is easy:
class Foo{...}
class Bar{...}
if (typeof module !== 'undefined') module.exports = { Foo, Bar };
or
class Buzz{...}
if (typeof module !== 'undefined') module.exports = Buzz;
However, trying to use require in all the files was an issue as the browser would complain about variables being already declared even when enclosed in an if block such as:
if (typeof require !== 'undefined') {
var {Foo,Bar} = require('./foobar.js');
}
So I got rid of the require part in the files and set up a mocha.opts file in my test folder with this content. The paths are relative to the root folder:
--require test/mocha.opts.js
mocha.opts.js content. The paths are relative to the location of the file:
global.assert = require('assert');
global.Foo = require("../foobar.js").Foo;
global.Bar = require("../foobar.js").Bar;
global.Buzz = require("../buzz.js");