前端优化是尽量减少http请求，所以我们需要尽量合并压缩文件，然后调用压缩后的文件，比如多个CSS文件压缩成一个，多个js文件合并压缩等，usemin能够自动在html中使用压缩后的文件，达到上面的目的。
上图是完整打包后的文件目录，原始目录是assets,打包发布的文件是dist.
gruntfile.js文件内容：
module.exports = function(grunt) { grunt.config.init({ clean:{ src:"dist/" }, useminPRepare: { html: 'index.html', options: { dest: 'dist' } }, usemin: { html: ['dist/index.html'] }, uglify: { 'dist/js/app.min.js': ['assets/js/*.js'] }, copy: { html: { src: './index.html', dest: 'dist/index.html' } }, cssmin:{ 'dist/css/app.min.css': ['assets/css/*.css'] } }); grunt.loadNpmTasks('grunt-contrib-clean'); grunt.loadNpmTasks('grunt-contrib-copy'); grunt.loadNpmTasks('grunt-contrib-uglify'); grunt.loadNpmTasks('grunt-contrib-concat'); grunt.loadNpmTasks('grunt-contrib-cssmin'); grunt.loadNpmTasks('grunt-usemin'); grunt.registerTask('default',[ 'clean', 'copy:html', 'useminPrepare', 'uglify', 'cssmin', 'usemin' ]);}
原始的index.html
<!DOCTYPE html><html> <head> <title>Usemin test</title> <!-- build:css dist/css/app.min.css --> <link rel="stylesheet" type="text/css" href="./assets/css/style.css" media="screen" /> <!-- endbuild --> </head> <body> </body> <!-- build:js dist/js/app.min.js --> <script src="./assets/js/foo.js"></script> <script src="./assets/js/bar.js"></script> <!-- endbuild --> </html>
打包后的index.html
<!DOCTYPE html><html> <head> <title>Usemin test</title> <link rel="stylesheet" href="dist/css/app.min.css" media="screen"/> </head> <body> </body> <script src="dist/js/app.min.js"></script></html>
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