How to introduce third-party libraries with webpack and precautions (code examples)

The content of this article is about the methods and precautions (code examples) for introducing third-party libraries in webpack. It has certain reference value. Friends in need can refer to it. I hope it will be helpful to you.

Under normal circumstances, we don’t have to worry about the third-party libraries used, which can’t be found in the npm management repository.

If you need a certain library, such as jquery, you can directly run the npm install jquery script command to install the dependencies required for this project;

Then, in the module file using jquery, pass Import $ from 'jquery' or var $ = require('jquery') to introduce.

This is a common way to introduce third-party libraries into projects built with webpack.

Note: In order to better demonstrate the sample code, the example is based on the nodemon article.

However, in different scenarios, there are different requirements for projects built by webpack:

The size of the project is small enough (cdn)

If it is the processing method of webapck, you can refer to the article webapck - Minimizing the Build Output.

Use non-webapck processing methods, such as CDN.

The operation is also very simple. If you use html-webpack-plugin, directly introduce a third-party library (such as: jquery) on a certain CDN (such as: boot CDN) into the template file template/index.html. , the reference code is as follows:

nbsp;html>


    <meta>
    <title>third party</title>


    <script></script>

Then, use jquery in module.js, the reference code is as follows:

require('./module.css');
module.exports = function() {
    $(document.body).append('<h1 id="hello-webpack">hello webpack</h1>')    
}

Finally, run npm run test. After the build is completed, you will see the words hello webpack in the browser with a red page effect in the background.

Use third-party libraries (provide-plugin or imports-loader) in the global environment

In order to avoid using third-party libraries every time, you need to use import or require( ) refers to them and can be defined as global variables.

The built-in plug-in of webpack's ProvidePlugin can solve this problem. For details, please refer to the introduction of ProvidePlugin.

To avoid conflicts with jquery referenced by cdn, lodash is used here.

First, install lodash dependency, the command is as follows:

yarn add lodash --dev

Then, in webpack.config.js, add the following code:

new webpack.ProvidePlugin({
        _: 'lodash'
}),

Secondly, in module.js Add the following code:

...
var arr = [1, 2, 3, 4, 5 ,6];
// provide-plugin
$(document.body).append('<h1 id="concat-arr">' + _.concat(arr, '~') + '</h1>');
...

Finally, run the npm run test script command. After the build is completed, you can add 1,2,3,4,5,6,~ to the browser page.

If you want to specify that a certain tool function of lodash can be used globally, such as: _.concat,

First, modify webapck.config.js as follows, the code is as follows:

...
new webpack.ProvidePlugin({
        // _: 'lodash',
        _concat: ['lodash', 'concat']
}),
...

Then, modify module.js, the code is as follows:

...
var arr = [1, 2, 3, 4, 5 ,6];
// provide-plugin
// $(document.body).append('<h1 id="concat-arr">' + _.concat(arr, '~') + '</h1>');
$(document.body).append('<h1 id="concat-arr">' + _concat(arr, '~') + '</h1>');
...

If you don’t like to use plug-ins, you can also consider using import-loader, which can also achieve the same purpose.

In order to avoid unnecessary interference, you can use underscore to demonstrate.

First, install the imports-loader dependency, the command is as follows:

yarn add imports-loader --dev

Then, install the underscore dependency, the command is as follows:

yarn add underscore

Secondly, add in webapck.config.js The following code:

...
module: {
        rules: [
                {
                        test: require.resolve('underscore'),
                        use: 'imports-loader?_=underscore'
                },
                ...
        ]
},
...

Note: Both underscore and lodash are developed using the singleton model. The names of their instantiated constructors are both _. In order to distinguish them, one of them needs to be changed. . It is a bit difficult for imports-loader to alias this logo, but provide-plugin does not have this problem and can set a personalized alias.

Modify webpack.config.js, the code is as follows:

new webpack.ProvidePlugin({
        // _: 'lodash',
        // _concat: ['lodash', 'concat'],
        __: 'lodash'
}),

Can be distinguished between lodash defined as __ and underscore_.

Then, modify module.js, the code is as follows:

...
// provide-plugin
// $(document.body).append('<h1 id="concat-arr">' + _.concat(arr, '~') + '</h1>');
// $(document.body).append('<h1 id="concat-arr">' + _concat(arr, '~') + '</h1>');
$(document.body).append('<h1 id="concat-arr">' + __.concat(arr, '~') + '</h1>');
...

Finally, save all the files, you can see similar results in the browser (after saving, nodemon will automatically start the browser) .

cdn and externals

I encountered some problems with externals before. Why do I need to explain them in detail because many people don’t understand what they are used for.

Scene reproduction:

Before, there was a project that used jquery. Because this library is relatively classic, it is frequently referenced in various modules of the application. The method of use is as follows:

import $ from 'jquery'

or

var $ = require('jquery')

The result is that after the build is completed, the file is relatively large. Then consider using a CDN, as described above. In this way, you need to delete the import or require references and delete the installed jquery dependency. However, because the project structure is relatively messy and there are many modules, in order to avoid the problem of less or missed changes, it will cause application errors. what can we do about it?

Some people say that if the jquery dependency is not deleted, the purpose of using cdn will be meaningless. Using external can solve this problem.

You can add the following code to the module.js file:

...
var $ = require('jquery')
...

Then, save the file and find that the build output prompts the following error:

ERROR in ./module.js
Module not found: Error: Can't resolve 'jquery' in 'E:\workspace\me\webpack-play\demo\example-1'
 @ ./module.js 3:0-23
 @ ./main.js
 @ multi (webpack)-dev-server/client?http://localhost:8080 ./main.js

in module module.js jquery cannot be parsed.

Next, add the following code to webpack.config.js:

externals: { 
    jquery: 'jQuery',
    jquery: '$'
},

where jquery represents jquery in require('jquery'), and jQuery and $ represent jquery The library itself provides instantiation identifiers. CDNization of other libraries, modifications similar to jquery.

However, if you decide to use cdn at the beginning of the project, do not use var $ = require('jquery') or import $ from 'jquery'; in a module that uses jquery, although this will not cause an error. , but if for some reason, jquery dependency may be introduced later, then you must use var $ = require('jquery') or import $ from 'jquery';.

Reference source code

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