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【基本解决】Webpack中url-loader和file-loader区别以及到底用哪个

Webpack crifan 1968浏览 0评论

折腾:

【已解决】wepack打包时出错:Module parse failed jpg Unexpected character

期间,知道是需要使用可以加载png,jpg等图片的loader,但是不知道对于url-loader和file-loader到底该用哪个,以及两者有何区别。

webpack url-loader vs file-loader

User file-loader and url-loader together for same file types? · Issue #653 · webpack/webpack

DataUrl

【已解决】url-loader中的DataUrl的含义

然后又发现一个专门加载图片的:

tcoopman/image-webpack-loader: Image loader module for webpack

那到底用哪个??

算了,还是先搞清楚url-loader和file-loader再说。

webpack-contrib/url-loader: url loader module for webpack

“If the file is greater than the limit (in bytes) the file-loader is used and all query parameters are passed to it.”

javascript – (Webpack) Using the url-loader or file-loader, do I really have to include a require() in my .js for every static image I want to include? – Stack Overflow

petehunt/webpack-howto

babel/babel-loader: Webpack plugin for Babel

Webpack 入门指迷 – 题叶 – SegmentFault

“这个 loader 实际上是对 file-loader 的封装”

url-loader

“The url-loader works like the file-loader, but can return a DataURL if the file is smaller than a byte limit.”

file-loader

➜  react-hot-boilerplate git:(master) ✗ npm install –save-dev url-loader
npm WARN babel-loader@6.2.10 requires a peer of webpack@1 || 2 || ^2.1.0-beta || ^2.2.0-rc but none was installed.
npm WARN react-dom@15.6.1 requires a peer of react@^15.6.1 but none was installed.
npm WARN url-loader@0.5.9 requires a peer of file-loader@* but none was installed.
added 2 packages in 11.566s

webpack-contrib/file-loader: file loader for webpack

“By default the filename of the resulting file is the MD5 hash of the file’s contents with the original extension of the required resource.”

➜  react-hot-boilerplate git:(master) ✗ npm install –save-dev file-loader
npm WARN babel-loader@6.2.10 requires a peer of webpack@1 || 2 || ^2.1.0-beta || ^2.2.0-rc but none was installed.
npm WARN react-dom@15.6.1 requires a peer of react@^15.6.1 but none was installed.
added 2 packages in 10.553s

结果期间遇到:

【已解决】Webpack打包出错:ERROR in Entry module not found Cannot resolve file or directory

【总结】

先解释背景:

(1)DataUrl和limit

url-loader中的url,和代码里面的url(比如:background-image: url(‘assets/img/user1-128×128.jpg’))完全没有关系。

url-loader中的url,指的是DataUrl中的url,支持url(…)和require(…)

另外,实际上css-loader会把url(…)转换为require(…)的。

再说:url-loader和file-loader区别

url-loader是对于file-loader的封装,且多了个功能,可以设置limit,当文件大小小于limit时,自动转换为DataURL,大于等于limit时,按照正常文件加载。

换句话说:那就可以不用file-loader了。

但是对于之前一个项目配置了:

      {
        test: /\.(svg|woff2?|ttf|eot|jpe?g|png|gif)(\?.*)?$/i,
        use: ENV===’production’ ? ‘file-loader’ : ‘url-loader’
      }

即对于生产环境中用file-loader,对于开发环境用url-loader,不知道是什么特殊考虑。

有点清楚了:

因为生产环境中,未了防治缓存问题,尽量用hash名作为文件名,包括图片的文件名,所以此处,当生产环境时,生成的图片,都是类似于:

8c4a576e6aa3ae896bfdc89084df6599.png

不过呢:

url-loader是基于file-loader封装的,所以:

url-loader=file-loader + limit功能

且由于url-loader中都说了:

当设置了limit后,大于limit的文件,则把对应的(query中配置的)参数传递给file-loader,所以此处,无序file-loader,直接用url-loader即可。

经过实际测试,url-loader也支持(file-loader本身就有的)定义文件名的功能。

所以此处的:

        use: isProd ?
          {
            loader: ‘file-loader’,
            query: {
              // name: ‘[path][name].[ext]?[md5:hash:base64:6]’
              //name: ‘[path][name]_[md5:hash:base64:6].[ext]’
              name: ‘[name]_[md5:hash:base64:6].[ext]’
            }
          } :
          {
            loader: ‘url-loader’,
            query: {
              // inline base64 DataURL for <=2KB images, direct URLs for the rest
              limit: 2048,
            }
          }

可以改为:

        use :
          {
            loader: ‘url-loader’,
            query: {
              // inline base64 DataURL for <=2KB images, direct URLs for the rest
              limit: 2048,
              name: ‘[name]_[md5:hash:base64:6].[ext]’
            }
          }

即可实现:

对于img的src的图片的代码:

<div className=”demo_image” />
.demo_image {
    width: 128px;
    height: 128px;
    background-image: url(‘assets/img/user1-128×128.jpg’)
}

当文件小于2048 byte=2KB时,background-image会被自动变成这种:

url(data:image/jpeg;base64,/9j/4AAQSkZJRg…………..14ioBcss/9k=)

之类的Data URL。

否则就当做正常的文件被加载,生成的文件名类似于:

user1-128x128_vykxhX.jpg

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