Web Front-end
JS Tutorial
Using import and require in JavaScript to implement principle analysis after packaging
Using import and require in JavaScript to implement principle analysis after packaging
This article mainly introduces the analysis of the principles of using import and require packaging in JavaScript. Friends in need can refer to it
Foreword:
I used ES6 to write code before, and I packaged it with webpack and put it online. There was no problem at all. I also saw the packaged code. It was very messy and I didn’t dare to see what was going on. After loading, it ran!
Today, let’s use an example to understand the code before and after packaging!
1. Create a folder and create two folders in it, the app folder and the public folder. The app folder uses To store the original data and the JavaScript module we will write, the public folder is used to store files that will be read by the browser (including js files generated using webpack packaging and an index.html file). Next we create three more files:
index.html -- placed in the public folder;
Greeter.js -- Place it in the app folder;
main.js -- Place it in the app folder;
The project structure is as shown below Show
Project structure
We write the most basic html code in the index.html file. Its purpose here is to introduce the packaged js file (here we First name the packaged js file bundle.js (we will talk about it in detail later).
<!-- index.html --> <!DOCTYPE html> <html lang="en"> <head> <meta charset="utf-8"> <title>sample Project</title> </head> <body> <p id='root'> </p> <script src="bundle.js"></script> </body> </html>
We define a function in Greeter.js that returns an html element containing greeting information, and export this function as a module according to the CommonJS specification:
// Greeter.js
exports.greet= function() {
var greet = document.createElement('p');
greet.textContent = "Hi there and greetings!";
return greet;
};
exports.USER_INFO = "userInfo";In the main.js file we write Enter the following code to insert the nodes returned by the Greeter module into the page.
//main.js
let {greeter,USER_INFO} =require('./Greeter.js');
console.log(USER_INFO);
document.querySelector("#root").appendChild(greeter());After packaging with webpack:
(function(modules){ var installedModules = {}; function __webpack_require__(moduleId) {
if (installedModules[moduleId]) {
return installedModules[moduleId].exports;
}
var module = installedModules[moduleId] = {
i: moduleId,
l: false,
exports: {}
};
modules[moduleId].call(module.exports, module, module.exports, __webpack_require__);
module.l = true;
return module.exports;
}
__webpack_require__.m = modules;
__webpack_require__.c = installedModules;
__webpack_require__.d = function(exports, name, getter) {
if (!__webpack_require__.o(exports, name)) {
Object.defineProperty(exports, name, {
configurable: false,
enumerable: true,
get: getter
});
}
};
__webpack_require__.n = function(module) {
var getter = module && module.__esModule ?
function getDefault() {
return module['default'];
}:
function getModuleExports() {
return module;
};
__webpack_require__.d(getter, 'a', getter);
return getter;
};
__webpack_require__.o = function(object, property) {
return Object.prototype.hasOwnProperty.call(object, property);
};
__webpack_require__.p = "";
return __webpack_require__(__webpack_require__.s = 0);
})
(
[
(function(module, exports, __webpack_require__) {
//main.js
let {
greeter,
USER_INFO
} = __webpack_require__(1);
console.log(USER_INFO);
document.querySelector("#root").appendChild(greeter());
}),
(function(module, exports) {
// Greeter.js
exports.greet = function() {
var greet = document.createElement('p');
greet.textContent = "Hi there and greetings!";
return greet;
};
exports.USER_INFO = "userInfo";
})
]);The first layer is wrapped with the immediate execution function (bold content). The parameter is an array, and each item in the array is the corresponding module. Each module is wrapped in (function(module, exports, __webpack_require__) {//module content});
Execute the function immediately return __webpack_require__(__webpack_require__.s = 0 );
That is, execute the first module main.js in the passed array
Mount each module after running to installedModules = {} Above, when this module is needed next time, it will directly return to the current module and no longer run the code block!
Next, change the require to import and see how to implement it after packaging
We will Greeter. The js information is changed to the following:
// Greeter.js
export default function() {
var greet = document.createElement('p');
greet.textContent = "Hi there and greetings!";
return greet;
};
export const USER_INFO = "userInfo";
main.js 文件中的代码，修改后
//main.js
import greet,{USER_INFO} from './Greeter.js';
console.log(USER_INFO);
document.querySelector("#root").appendChild(greet());Then we package it again:
(function(modules) {
var installedModules = {};
function __webpack_require__(moduleId) {
if (installedModules[moduleId]) {
return installedModules[moduleId].exports;
}
var module = installedModules[moduleId] = {
i: moduleId,
l: false,
exports: {}
};
modules[moduleId].call(module.exports, module, module.exports, __webpack_require__);
module.l = true;
return module.exports;
}
__webpack_require__.m = modules;
__webpack_require__.c = installedModules;
__webpack_require__.d = function(exports, name, getter) {
if (!__webpack_require__.o(exports, name)) {
Object.defineProperty(exports, name, {
configurable: false,
enumerable: true,
get: getter
});
}
};
__webpack_require__.n = function(module) {
var getter = module && module.__esModule ?
function getDefault() {
return module['default'];
}: function getModuleExports() {
return module;
};
__webpack_require__.d(getter, 'a', getter);
return getter;
};
__webpack_require__.o = function(object, property) {
return Object.prototype.hasOwnProperty.call(object, property);
};
__webpack_require__.p = "";
return __webpack_require__(__webpack_require__.s = 0);
})([(function(module, __webpack_exports__, __webpack_require__) {
"use strict";
Object.defineProperty(__webpack_exports__, "__esModule", {
value: true
});
var __WEBPACK_IMPORTED_MODULE_0__Greeter_js__ = __webpack_require__(1);
//main.js
console.log(__WEBPACK_IMPORTED_MODULE_0__Greeter_js__["a"]);
document.querySelector("#root").appendChild(Object(__WEBPACK_IMPORTED_MODULE_0__Greeter_js__["b"])());
}),
(function(module, __webpack_exports__, __webpack_require__) {
"use strict";
__webpack_exports__["b"] = (function() {
var greet = document.createElement('p');
greet.textContent = "Hi there and greetings!";
return greet;
});;
const USER_INFO = "userInfo";
__webpack_exports__["a"] = USER_INFO;
})]);The above is what I compiled for everyone. I hope it will be helpful to everyone in the future.
Related articles:
vue2.0 Method to implement page navigation prompt guidance
vue2.0 based on status value Style change display method
How to use Vuex to implement a note application
The above is the detailed content of Using import and require in JavaScript to implement principle analysis after packaging. For more information, please follow other related articles on the PHP Chinese website!
Hot AI Tools
Undresser.AI Undress
AI-powered app for creating realistic nude photos
AI Clothes Remover
Online AI tool for removing clothes from photos.
Undress AI Tool
Undress images for free
Clothoff.io
AI clothes remover
AI Hentai Generator
Generate AI Hentai for free.
Hot Article
Hot Tools
Notepad++7.3.1
Easy-to-use and free code editor
SublimeText3 Chinese version
Chinese version, very easy to use
Zend Studio 13.0.1
Powerful PHP integrated development environment
Dreamweaver CS6
Visual web development tools
SublimeText3 Mac version
God-level code editing software (SublimeText3)
Hot Topics
How to implement an online speech recognition system using WebSocket and JavaScript
Dec 17, 2023 pm 02:54 PM
How to use WebSocket and JavaScript to implement an online speech recognition system Introduction: With the continuous development of technology, speech recognition technology has become an important part of the field of artificial intelligence. The online speech recognition system based on WebSocket and JavaScript has the characteristics of low latency, real-time and cross-platform, and has become a widely used solution. This article will introduce how to use WebSocket and JavaScript to implement an online speech recognition system.
WebSocket and JavaScript: key technologies for implementing real-time monitoring systems
Dec 17, 2023 pm 05:30 PM
WebSocket and JavaScript: Key technologies for realizing real-time monitoring systems Introduction: With the rapid development of Internet technology, real-time monitoring systems have been widely used in various fields. One of the key technologies to achieve real-time monitoring is the combination of WebSocket and JavaScript. This article will introduce the application of WebSocket and JavaScript in real-time monitoring systems, give code examples, and explain their implementation principles in detail. 1. WebSocket technology
How to implement an online reservation system using WebSocket and JavaScript
Dec 17, 2023 am 09:39 AM
How to use WebSocket and JavaScript to implement an online reservation system. In today's digital era, more and more businesses and services need to provide online reservation functions. It is crucial to implement an efficient and real-time online reservation system. This article will introduce how to use WebSocket and JavaScript to implement an online reservation system, and provide specific code examples. 1. What is WebSocket? WebSocket is a full-duplex method on a single TCP connection.
How to use JavaScript and WebSocket to implement a real-time online ordering system
Dec 17, 2023 pm 12:09 PM
Introduction to how to use JavaScript and WebSocket to implement a real-time online ordering system: With the popularity of the Internet and the advancement of technology, more and more restaurants have begun to provide online ordering services. In order to implement a real-time online ordering system, we can use JavaScript and WebSocket technology. WebSocket is a full-duplex communication protocol based on the TCP protocol, which can realize real-time two-way communication between the client and the server. In the real-time online ordering system, when the user selects dishes and places an order
JavaScript and WebSocket: Building an efficient real-time weather forecasting system
Dec 17, 2023 pm 05:13 PM
JavaScript and WebSocket: Building an efficient real-time weather forecast system Introduction: Today, the accuracy of weather forecasts is of great significance to daily life and decision-making. As technology develops, we can provide more accurate and reliable weather forecasts by obtaining weather data in real time. In this article, we will learn how to use JavaScript and WebSocket technology to build an efficient real-time weather forecast system. This article will demonstrate the implementation process through specific code examples. We
Simple JavaScript Tutorial: How to Get HTTP Status Code
Jan 05, 2024 pm 06:08 PM
JavaScript tutorial: How to get HTTP status code, specific code examples are required. Preface: In web development, data interaction with the server is often involved. When communicating with the server, we often need to obtain the returned HTTP status code to determine whether the operation is successful, and perform corresponding processing based on different status codes. This article will teach you how to use JavaScript to obtain HTTP status codes and provide some practical code examples. Using XMLHttpRequest
What are the uses of require?
Nov 27, 2023 am 10:03 AM
Usage of require: 1. Introduce modules: In many programming languages, require is used to introduce external modules or libraries so that the functions they provide can be used in the program. For example, in Ruby, you can use require to load third-party libraries or modules; 2. Import classes or methods: In some programming languages, require is used to import specific classes or methods so that they can be used in the current file; 3. Perform specific tasks: In some programming languages or frameworks, require is used to perform specific tasks or functions.
How to get HTTP status code in JavaScript the easy way
Jan 05, 2024 pm 01:37 PM
Introduction to the method of obtaining HTTP status code in JavaScript: In front-end development, we often need to deal with the interaction with the back-end interface, and HTTP status code is a very important part of it. Understanding and obtaining HTTP status codes helps us better handle the data returned by the interface. This article will introduce how to use JavaScript to obtain HTTP status codes and provide specific code examples. 1. What is HTTP status code? HTTP status code means that when the browser initiates a request to the server, the service
