Grunt concat + uglify with sourcemaps

You need to enable source maps on both the concat and uglify tasks, and you must specify the sourceMapIn option for the uglify task.

Here’s a sample grunt config:

concat : {
  options : {
    sourceMap :true
  },
  dist : {
    src  : ['www/js/**/*.js'],
    dest : '.tmp/main.js'
  }
},
uglify : {
  options : {
    sourceMap : true,
    sourceMapIncludeSources : true,
    sourceMapIn : '.tmp/main.js.map'
  },
  dist : {
    src  : '<%= concat.dist.dest %>',
    dest : 'www/main.min.js'
  }
}