search
HomeWeb Front-endJS TutorialInstructions for using loader mechanism in webpack source code

This time I will bring you the instructions for using the loader mechanism in the webpack source code. What are the precautions for using the loader mechanism in the webpack source code. The following is a practical case, let's take a look.

Loader concept

Loader is used to load and process various forms of resources. It is essentially a function that accepts files as parameters and returns the converted structure.

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

The difference between loader and plugin

The plugin mechanism was introduced in the previous article, and the loader, the object of today's study, together they have greatly expanded webpack function. The difference between them is that the loader is used to convert the source code of the module, while the purpose of the plug-in is to solve other things that the loader cannot achieve. Why do you say so much? Because the plugin can be called at any stage, it can further process the output of the Loader across the Loader, trigger events during the build run, execute pre-registered callbacks, and use the compilation object to do some lower-level things.

loader usage

Configuration

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

Inline

import Styles from 'style-loader!css-loader?modules!./styles.css';
CLI

webpack --module-bind 'css=style-loader!css-loader'
Explain that the above three methods of use are to execute a set of chained loaders in order from right to left. The first loader in the loader chain returns the value to the next loader. First use css-loader to parse the css content specified in the @import and url() paths, and then use style-loader to insert the original CSS code into a style tag on the page.

loader implementation

//将css插入到head标签内部
module.exports = function (source) {
  let script = (`
   let style = document.createElement("style");
   style.innerText = ${JSON.stringify(source)};
   document.head.appendChild(style);
  `);
  return script;
}
//使用方式1
resolveLoader: {
  modules: [path.resolve('node_modules'), path.resolve(dirname, 'src', 'loaders')]
},
{
  test: /\.css$/,
  use: ['style-loader']
},
//使用方式2
//将自己写的loaders发布到npm仓库,然后添加到依赖,按照方式1中的配置方式使用即可
Description The above is a simple loader implementation, executed in a synchronous manner, which is equivalent to realizing the function of style-loader.

Loader Principle

function iteratePitchingLoaders(options, loaderContext, callback) {
  var currentLoaderObject = loaderContext.loaders[loaderContext.loaderIndex];
  // load loader module
  loadLoader(currentLoaderObject, function(err) {
    var fn = currentLoaderObject.pitch;
    runSyncOrAsync(
      fn,
      loaderContext, [loaderContext.remainingRequest, loaderContext.previousRequest, currentLoaderObject.data = {}],
      function(err) {
        if(err) return callback(err);
        var args = Array.prototype.slice.call(arguments, 1);
        if(args.length > 0) {
          loaderContext.loaderIndex--;
          iterateNormalLoaders(options, loaderContext, args, callback);
        } else {
          iteratePitchingLoaders(options, loaderContext, callback);
        }
      }
    );
  });
}
Description The above are the key steps for loader execution in the webpack source code. The loader is executed recursively. The execution process is similar to express

middlewareMechanism

Reference source code

  1. webpack: "4.4.1"

  2. ##webpack- cli: "2.0.13"
  3. I believe you have mastered the method after reading the case in this article. For more exciting information, please pay attention to other related articles on the PHP Chinese website!

Recommended reading:

JS analysis of steps to implement dynamic progress bar


js css to achieve typing effect with controllable speed on the page

The above is the detailed content of Instructions for using loader mechanism in webpack source code. For more information, please follow other related articles on the PHP Chinese website!

Statement
The content of this article is voluntarily contributed by netizens, and the copyright belongs to the original author. This site does not assume corresponding legal responsibility. If you find any content suspected of plagiarism or infringement, please contact admin@php.cn
Python vs. JavaScript: Community, Libraries, and ResourcesPython vs. JavaScript: Community, Libraries, and ResourcesApr 15, 2025 am 12:16 AM

Python and JavaScript have their own advantages and disadvantages in terms of community, libraries and resources. 1) The Python community is friendly and suitable for beginners, but the front-end development resources are not as rich as JavaScript. 2) Python is powerful in data science and machine learning libraries, while JavaScript is better in front-end development libraries and frameworks. 3) Both have rich learning resources, but Python is suitable for starting with official documents, while JavaScript is better with MDNWebDocs. The choice should be based on project needs and personal interests.

From C/C   to JavaScript: How It All WorksFrom C/C to JavaScript: How It All WorksApr 14, 2025 am 12:05 AM

The shift from C/C to JavaScript requires adapting to dynamic typing, garbage collection and asynchronous programming. 1) C/C is a statically typed language that requires manual memory management, while JavaScript is dynamically typed and garbage collection is automatically processed. 2) C/C needs to be compiled into machine code, while JavaScript is an interpreted language. 3) JavaScript introduces concepts such as closures, prototype chains and Promise, which enhances flexibility and asynchronous programming capabilities.

JavaScript Engines: Comparing ImplementationsJavaScript Engines: Comparing ImplementationsApr 13, 2025 am 12:05 AM

Different JavaScript engines have different effects when parsing and executing JavaScript code, because the implementation principles and optimization strategies of each engine differ. 1. Lexical analysis: convert source code into lexical unit. 2. Grammar analysis: Generate an abstract syntax tree. 3. Optimization and compilation: Generate machine code through the JIT compiler. 4. Execute: Run the machine code. V8 engine optimizes through instant compilation and hidden class, SpiderMonkey uses a type inference system, resulting in different performance performance on the same code.

Beyond the Browser: JavaScript in the Real WorldBeyond the Browser: JavaScript in the Real WorldApr 12, 2025 am 12:06 AM

JavaScript's applications in the real world include server-side programming, mobile application development and Internet of Things control: 1. Server-side programming is realized through Node.js, suitable for high concurrent request processing. 2. Mobile application development is carried out through ReactNative and supports cross-platform deployment. 3. Used for IoT device control through Johnny-Five library, suitable for hardware interaction.

Building a Multi-Tenant SaaS Application with Next.js (Backend Integration)Building a Multi-Tenant SaaS Application with Next.js (Backend Integration)Apr 11, 2025 am 08:23 AM

I built a functional multi-tenant SaaS application (an EdTech app) with your everyday tech tool and you can do the same. First, what’s a multi-tenant SaaS application? Multi-tenant SaaS applications let you serve multiple customers from a sing

How to Build a Multi-Tenant SaaS Application with Next.js (Frontend Integration)How to Build a Multi-Tenant SaaS Application with Next.js (Frontend Integration)Apr 11, 2025 am 08:22 AM

This article demonstrates frontend integration with a backend secured by Permit, building a functional EdTech SaaS application using Next.js. The frontend fetches user permissions to control UI visibility and ensures API requests adhere to role-base

JavaScript: Exploring the Versatility of a Web LanguageJavaScript: Exploring the Versatility of a Web LanguageApr 11, 2025 am 12:01 AM

JavaScript is the core language of modern web development and is widely used for its diversity and flexibility. 1) Front-end development: build dynamic web pages and single-page applications through DOM operations and modern frameworks (such as React, Vue.js, Angular). 2) Server-side development: Node.js uses a non-blocking I/O model to handle high concurrency and real-time applications. 3) Mobile and desktop application development: cross-platform development is realized through ReactNative and Electron to improve development efficiency.

The Evolution of JavaScript: Current Trends and Future ProspectsThe Evolution of JavaScript: Current Trends and Future ProspectsApr 10, 2025 am 09:33 AM

The latest trends in JavaScript include the rise of TypeScript, the popularity of modern frameworks and libraries, and the application of WebAssembly. Future prospects cover more powerful type systems, the development of server-side JavaScript, the expansion of artificial intelligence and machine learning, and the potential of IoT and edge computing.

See all articles

Hot AI Tools

Undresser.AI Undress

Undresser.AI Undress

AI-powered app for creating realistic nude photos

AI Clothes Remover

AI Clothes Remover

Online AI tool for removing clothes from photos.

Undress AI Tool

Undress AI Tool

Undress images for free

Clothoff.io

Clothoff.io

AI clothes remover

AI Hentai Generator

AI Hentai Generator

Generate AI Hentai for free.

Hot Article

R.E.P.O. Energy Crystals Explained and What They Do (Yellow Crystal)
4 weeks agoBy尊渡假赌尊渡假赌尊渡假赌
R.E.P.O. Best Graphic Settings
4 weeks agoBy尊渡假赌尊渡假赌尊渡假赌
R.E.P.O. How to Fix Audio if You Can't Hear Anyone
4 weeks agoBy尊渡假赌尊渡假赌尊渡假赌
WWE 2K25: How To Unlock Everything In MyRise
1 months agoBy尊渡假赌尊渡假赌尊渡假赌

Hot Tools

MinGW - Minimalist GNU for Windows

MinGW - Minimalist GNU for Windows

This project is in the process of being migrated to osdn.net/projects/mingw, you can continue to follow us there. MinGW: A native Windows port of the GNU Compiler Collection (GCC), freely distributable import libraries and header files for building native Windows applications; includes extensions to the MSVC runtime to support C99 functionality. All MinGW software can run on 64-bit Windows platforms.

mPDF

mPDF

mPDF is a PHP library that can generate PDF files from UTF-8 encoded HTML. The original author, Ian Back, wrote mPDF to output PDF files "on the fly" from his website and handle different languages. It is slower than original scripts like HTML2FPDF and produces larger files when using Unicode fonts, but supports CSS styles etc. and has a lot of enhancements. Supports almost all languages, including RTL (Arabic and Hebrew) and CJK (Chinese, Japanese and Korean). Supports nested block-level elements (such as P, DIV),

Safe Exam Browser

Safe Exam Browser

Safe Exam Browser is a secure browser environment for taking online exams securely. This software turns any computer into a secure workstation. It controls access to any utility and prevents students from using unauthorized resources.

SublimeText3 English version

SublimeText3 English version

Recommended: Win version, supports code prompts!

SublimeText3 Mac version

SublimeText3 Mac version

God-level code editing software (SublimeText3)