I know that if there are multiple JS files to be rendered by the browser, which apparently have identifiers inside, the global scope is polluted by this identifiers. I also know that one way to avoid this is using modules which(in my understanding) are just objects which have the aformentioned identifiers as members, thus sort of imitating C++ namespaces. I am also learning Node.js and there is a built in module system which eases this task so my question is: how to use modules in js files that are sent to the browser to be rendered?
Thanks.
Tools like browserify and WebPack are exactly what you are looking for (I personally prefer browserify over WebPack). Have a look at this answer, it explains a lot of your concerns.
In Node.JS, you can export a module using module.exports keyword, but you cannot just import those modules in your browser by just requiring them in a <script> tag. That's because, the browser doesn't understand the module system and everything works in the context of a global window object there, so module.exports simply becomes window.module.exports which I'm sure you'll not want. Hence you use tools like browserify that process the Node.JS scripts into something that your browser will understand.
This problem is usually solved by module bundlers or module loaders (e.g Webpack, Browserify, RequireJS). They are able to understand relations between your JS modules, skip unused modules and produce output that just works in your browser. All of that without the need to worry too much about global scope if you follow some conventions.
Some time ago, before ES6, two different approaches to this problem were widely used:
CommonJS:
var module = require('my-module');
widely known from Node.js
AMD:
define(['jquery'] , function ($) {
return function () {};
});
Which was suited for browser usage since it by design supported asynchronous loading of modules.
Then ES6 was introduced with native support for modules:
import * as lib from 'lib';
Main problem with new technology in web is that you often have variety of browsers to support which for a long time prevented developers from using new features. Nowadays, we have code transpilers and sophisticated code bundlers (e.g. Webpack). With their help you can use latest version of language, compile and bundle your code and at the end single "bundle.js" file is emitted which supports older browsers at the cost of slower execution times.
Related
Create-React-App uses Babel that converts my ES6 modules to CommonJS module and Webpack will bundle everything in single file that my browser can understand.
1) Why not use CommonJS modules directly and use Webpack as bundler?
2) Now that ES6 modules are supported in browsers, why don't we transpile React CommonJS modules to ES6 modules.
Go to your Chrome console and type in require, you will get the message require not defined.
Our browser, in particular Chrome, has no idea what CommonJS is, it has no idea what modules are.
But if you are looking to remove those restrictions in your project, you can make use of Electron.
If you run require inside of the Electron browser window you will get this:
f require(path) {
try {
exports.requireDepth += 1;
return mod.require(path);
} finally {
exports.requireDepth -= 1;
}
}
Chrome the browser has no idea what the above is, but the Electron browser window does. It has some additional capabilities that Chrome does not.
The Electron browser has a MainWindow object which has access to all the available modules the belong to the Nodejs runtime and access to all modules inside the browser as well. So access to CommonJS as well as fs, crypto, etcetera.
You can do `require('fs') and access the filesystem directly from the Electron browser console.
In short, I am saying that with Electron you can directly require in modules like you want without having to use Webpack.
CommonJS code will not allow you to write code using imports, arrow functions, destructuring, generators, class etc... This makes your developer's life easy and I do see below advantages:
Less code more for same functionality.
Less time required for writing same functionality.
As of chrome 61 + can process your ES6 code but other browser will not be supporting it. So you need to transpile ES6 code to common js code so that it is consistent across browsers.
Quick question. I am a bit confused about ES2015(ES6).
Let's say I use Babel to compile to ES6 Javascript to compliant ES5 for current browsers.
The import/export functions are already available in ES6 by using Babel. So why would I need something like Browserify or Webpack if I were to simply use these just to bundle my modules, when ES6 could do it for me?
Everywhere I go I see people using Babel in combination with Browserify or Webpack. Although I know something like Webpack can be used for more, but I wonder if it is also possible to bundle files using the ES6 syntax.
I might be totally in the wrong here and I might have gotten lost in the Javascript Jungle of 2016, so I hope someone can clarifty this for me.
Edit
Am I right to assume that the native ES6 import / export functionality simply does not bundle files? From what I have read so far I think you still need to include all the separate Javascript files but you simply import modules into each-others namespace by using the native import functionality?
Yes, using babel to transpile your ES6 imports into ES5 will work.
However, one advantage of using webpack is that creates one static file to be served up in your production environment.
Pre-ES6 has no native module system, so there are multiple systems constructed in userland code (e.g. CommonJS / Node modules and AMD). Those are what Babel converts ES6 module syntax to (and yes, you're correct that ES6 module syntax has no native bundling story anyway). Browsers have no knowledge of those userland APIs. Node implements its module system by wrapping a "module" in a function that injects require() etc. In a browser require() would just be a reference error. Browserify (or another bundler) makes it work in the browser, and bundles a whole dependency graph into a single script. So if the code is for the browser you're likely going to want to bundle it. If it's for Node you may not need to.
The import/export functions
Not functions, declarations.
if I were to simply use these just to bundle my modules, when ES6 could do it for me?
I wonder if it is also possible to bundle files using the ES6 syntax.
Am I right to assume that the native ES6 import / export functionality simply does not bundle files?
Yes. There's no native way to bundle ES6 modules. You can transpile ES6 module syntax to something like Node modules and bundle those.
From what I have read so far I think you still need to include all the separate Javascript files but you simply import modules into each-others namespace by using the native import functionality?
It's important to realize that while the syntax is standardized, a lot of the behavior isn't. There's a Loader spec under development to specify how modules will actually be located and loaded.
See also https://stackoverflow.com/a/33044085/1034448.
I have a large project entirely built in JavaScript, I have an ordered and "inside modularized" 5k lines .js file that's the engine of whole site.
Now I have to make other site (extension of this one) in which I'll have to repeat a lot of code, my question is, I've seen lot of possibilities using Browserify, CommonJS, etc. But that's not what I'm searching, I'm searching modularize JavaScript just like C/C++, making #includes with the files of the functions or functionalities and reuse code like that. I'm already doing this including other JS files in HTML, but that JS files are only variables and some arrays, not functionality of the site.
I use jQuery too, in that large 5k lines .js file I have almost all inside the jQuery document.ready event, that's bringing trouble too, because I'll have to make a document.ready event for every file?
I need some orientation please
CommonJS will let you require() modules, this is the foundation for the NodeJS module system. Browserify simplifies this implementation for use in browsers and even allows you to require Node modules (as long as they don't depend on binaries, the file system and other features a browser doesn't support).
var lib = require('someLibrary');
ECMAScript6 (aka: ES6) brings imports to javascript. While browsers don't fully support ES6 yet, you can use Babel to "transpile" ES6 to ES5. This ES5 will take advantage of CommonJS to replicate the importing behaviour.
import { SomeClass, someFunction, someValue } from 'some/library';
In all cases, your javascript will require some kind of pre-processing to transpile it into javscript a browser can understand. This usually means taking all your separate source files and bundling them into a single minified bundle file. This reduces the number of requests the browser has to make.
To handle all this transpiling and bundling, several popular build systems exist including Grunt, Gulp and Webpack. Grunt is older and typically slower because of it's configuration-based design. Gulp is simpler and faster because it relies on NodeJS streams. Webpack is the newest and most powerful, but at the cost of complexity. For what you're hoping to do, I'd recommend looking at Webpack since it can modularize not only your javascript but your stylesheets and other web assets.
http://webpack.github.io/docs/tutorials/getting-started/
Use webpack to bundle your code http://webpack.github.io/docs/tutorials/getting-started/
According to this question How do I include a JavaScript file in another JavaScript file?. It seems a lots of people are interested in breaking big Javascript projects into small modules and export/import modules for code reuse.
After some research, import/export are designed for this feature. According to the references, they're initially defined in ES6.
Update
Latest version of main browsers shipped with this feature implemented. To have the latest status, please always refer to the References.
(If you're using nodejs, Modules (https://nodejs.org/dist/latest-v5.x/docs/api/modules.html) is the best aproach)
Refrerences:
https://developer.mozilla.org/en/docs/web/javascript/reference/statements/import
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/export
In the current versions of JS there are a few methods of doing this. Require uses the AMD design pattern, and is the standard for frontend dependency injection / module loading. Frameworks such as Angular use this method.
Here is a link to the require docs.
http://requirejs.org/
Time goes by... Today I would rather suggest using Babel (within browserify or webpack) to turn ES modules into plain old javascript.
Then you have the full power of import/export syntax.
Require/AMD/CommonJS is just getting deprecated anytime soon.
In ES6 each module is defined in its own file.
Does that mean that we will have to do multiple network calls for each javascript module if we go the es6 way?
Is there anyway to concatenate the module files essentially create one minified javascript file for the app in es6?
We can transpile the es6 code to es5 and concatenate the same.
But, without transpiling to es5, does it mean that to use modules, we won't be able to concatenate and minify all javascript files into one?
Bundling is the way to go.
Modern web applications consist of many, often small, modules. Loading
those modules over HTTP impacts performance negatively, because a
separate request is needed for each. Therefore, bundling multiple
modules as a single file has a long tradition in the web development
world. Current approaches are complex and error-prone and only work
for JavaScript. Therefore, the W3C Technical Architecture Group is
working on a new approach: Arbitrarily nested directories are archived
as a single package file. Browsers access files in the package via a
new kind of URL:
url-for-package SEPARATOR path-inside-package
Source: http://www.2ality.com/2013/11/es6-modules-browsers.html