Loader analysis of webpack3

What can webpack do? The answer given by the official website is, in one sentence, it makes everything simple! Various loaders emerge in endlessly, leaving us at a loss when building. Here, we summarize the full analysis of loaders. This article mainly introduces the full analysis of the loader of webpack3. The editor thinks it is quite good. Now I will share it with you and give you a reference. Let’s follow the editor to take a look, I hope it can help everyone.

Concept

loader, as the name suggests, loader, the English explanation is as follows:

Loaders are transformations that are applied on the source code of a module . They allow you to pre-process files as you import or “load” them. Thus, loaders are kind of like “tasks” in other build tools, and provide a powerful way to handle front-end build steps. Loaders can transform files from a different language (like TypeScript) to JavaScript, or inline images as data URLs. Loaders even allow you to do things like import CSS files directly from your JavaScript modules!

The Chinese translation is:

loader is used to convert the source code of the module. Loaders allow you to preprocess files when importing or "loading" modules. Therefore, loaders are similar to "tasks" in other build tools and provide a powerful way to handle front-end build steps. Loaders can convert files from different languages ​​(such as TypeScript) to JavaScript, or inline images to data URLs. The loader even allows you to import CSS files directly in JavaScript modules!

From this, we can see the powerful role of loader. Let’s analyze:

1. The role of conversion. Everything used in development is converted into files in required formats such as html+css+js+img, which are necessary for web page loading.

2. The conversion object is the source code. The loader only converts the source code. As for other functions, the plugins take over what it cannot do.

To summarize: loader, a loading machine, is like a soymilk machine. Put your ingredients and it will start working seriously!

Commonly used loaders

1、babel-loader

This package allows transpiling JavaScript files using Babel and webpack.

Load ES2015+ code, and then use Babel to translate to ES5

Installation:

npm install --save-dev babel-loader babel-core babel-preset-env webpack

Use:

{
 test: /\.js$/,
 exclude: /node_modules/,
 loader: 'babel-loader'
}

2、style-loader

Adds CSS to the DOM by injecting a c9ccee2e6ea535a969eb3f532ad9fe89 tag

Add the export of the module to the DOM as a style

Installation:

npm install style-loader --save-dev

It is recommended to use it together with css-loader

Use:

{
 test: /\.css$/,
 use: [
 'style-loader',
 'css-loader'
]
}

3, css-loader

After parsing the CSS file, use import to load it and return the CSS code

Installation:

npm install css-loader --save-dev

Use:

{
 test: /\.css$/,
 use: [ 'style-loader', 'css-loader' ]
}

4, less-loader

Load and translate LESS File

Installation:

##

npm install --save-dev less-loader less

Use:

{
 test: /\.less$/,
 exclude: /node_modules/,
 use: ExtractTextPlugin.extract(['css-loader', 'less-loader'])
}

5, url-loader

Loads files as base64 encoded URL

Process image files, but if the file is smaller than the limit, you can return data URL

Installation:

npm install --save-dev url-loader

Use:

{
 test: /\.(jpg|jpeg|png|gif)$/,
 loader: 'url-loader',
 options: {
   limit: 8192
 }
}

6. file-loader

Instructs webpack to emit the required object as file and to return its public URL

Processing font/ svg etc., sends the file to the output folder and returns the (relative) URL

Install:

npm install file-loader --save-dev

Use:

{
 test: /\.(woff|woff2|svg|eot|ttf)$/,
 use: 'file-loader'
}

7. vue-loader

Loading and translating Vue components

Installation:

npm install --save-dev vue-loader vue vue-template-compiler

Use:

{
 test: /\.vue$/,
 loader: 'vue-loader',
 options: {
   loaders: {
     less: ExtractTextPlugin.extract({
       use: ['css-loader', 'less-loader'],
       fallback: 'vue-style-loader'
     })
   }
 }
}

Related recommendations:

Detailed explanation of classloader based on Java class loading method

How to understand loader and plugin in webpack

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