refer to: https://github.com/tschaub/grunt-newer

这个技能是跟 团队的同学们 学来的。 ^_^ 

grunt-newer: 管理仅发生变化的文件。grunt-watch 能监控文件的变动. 它俩要配合使用。

安装：

1. 编辑 package.json ,

// package.json; 
'devDependencies': {
    "grunt-newer": "1.1.0"
    "grunt-contrib-watch": "~0.5.1",
}

$ npm install 

2. 然后，Gruntfile.coffee中，加上 watch 任务：

 
module.exports = (grunt) ->
  grunt.initConfig

    # 这个最重要。
    watch:
      options:
        nospawn: true
      views:
        files: ['src/**/*.jade']
        tasks: ['newer:jade']
      styles:
        files: ['src/**/*.stss']
        tasks: ['newer:stss']
      javascripts:
        files: ['src/**/*.coffee']
        tasks: ['newer:coffee']

    coffee:
      compile_multiple_files:
        options:
          bare: true
        files:
          # 1:1 的编译文件
          #'app/controllers/simulate_stocks.js': 'app/controllers/simulate_stocks.coffee'
          # 编译多个文件

          [
            expand: true
            flatten: true
            cwd: 'src/controllers/'
            src: ['*.coffee']
            dest: 'app/controllers/'
            ext: '.js'
          ]

      compile_flat_details:
        options:
          bare: true
        files:
          # 把多个文件合并
          'app/controllers/flatDetails.js': [
            'src/controllers/flat_details/1*.coffee'
            'src/controllers/flat_details/2*.coffee'
            'src/controllers/flat_details/3*.coffee'
          ]

      compile_diy_project:
        options:
          bare: true
        files:
          # 把多个文件合并
          'app/controllers/diyProject.js': [
            'src/controllers/diy_project/1*.coffee'
            'src/controllers/diy_project/2*.coffee'
            'src/controllers/diy_project/3*.coffee'
            'src/controllers/diy_project/4*.coffee'
            'src/controllers/diy_project/5*.coffee'
          ]

    jade:
      compile:
        options:
          pretty: true
        files: [
          expand: true
          src: ['views/*.jade']
          dest: 'app' # 写成  'app/views' 也行,
          cwd: 'src'  # 如果 dest是'app/views', 这里就要是 'src/views'
          ext: '.xml'
        ]

    stss:
      compile:
        files:[
          expand: true
          src: ['**/*.stss']
          dest: 'app/styles'
          cwd: 'src/styles'
          ext: '.tss'
        ]

  grunt.loadNpmTasks 'grunt-contrib-watch'
  grunt.loadNpmTasks 'grunt-newer'
  grunt.loadNpmTasks 'grunt-contrib-coffee'
  grunt.loadNpmTasks 'grunt-contrib-jade'
  grunt.loadNpmTasks 'grunt-stss'

  grunt.registerTask 'default', [ 'coffee', 'jade','stss' ]

3. 运行： $ grunt watch 

这样，你的每次改动，都会瞬间被监控到，然后调用对应的命令。例如，每改一个jade 文件，watch就会调用 jade 这个任务。