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UglifyJS2

JavaScript parser / mangler / compressor / beautifier toolkit UglifyJS — JavaScript parser, compressor, minifier written in JS

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Language : Javascript

http://lisperator.net/uglifyjs/

Uglify with SourceMaps while using grunt usemin and rev

I want to log javascript errors to server but the stacktrace is not useful with minified JS code. So I was thinking of using either Getsentry or Rollbar which shows proper stack trace with the help of sourcemaps. But I'm struggling to create sourcemap in first place.

I'm getting this error

"Destination (_build/js/app.js) not written because src files were empty."

Once it creates source map properly, there will be another problem i.e. rev will rename the file. I also need to leave the unminified concatenated file.

Below is my gruntfile.js (I've removed few bits out of it.)

module.exports = function(grunt) {

    grunt.initConfig({
        pkg: grunt.file.readJSON('package.json'),
        clean: {
            jsFolders: {
                src: [
                    '_build/js/ui',
                    '_build/js/vendor',
                    '_build/js/app',
                    '_build/js/*templates.js'
                ]
            },
            build: {
                src: ['_build/**/*']
            }
        },

        copy: {
            build: {
                files: [{
                    expand: true,
                    src: [
                        'index.html',
                        'img/**/*', //includes web.cofig also.
                        'img/**/*.svg',
                        '!img/**/*.psd',
                        'js/**/*', //includes web.cofig also.
                        'css/**/*', //includes web.cofig also.
                        '*.png',
                        'favicon.ico'
                    ],
                    dest: '_build/'
                }]
            },
        },

        rev: {
            option: {
                algorithm: 'sha1',
                length: 4
            },
            all: {
                files: {
                    src: [
                        '_build/**/*.{js,css,eot,ttf,woff}'
                    ]
                }
            }
        },

        useminPrepare: {
            html: ['_build/index.html']
        },

        usemin: {
            html: [
                '_build/index.html'
            ],
            css: [
                '_build/css/**/*.css'
            ]
        },

        uglify: {
            options: {
                sourceMap: '_build/js/app.js.map',
            },
            js: {
                files: {
                    '_build/js/app.js': ['_build/js/app.js']
                }
            }
        },

        cssmin: {
            minify: {
                expand: true,
                cwd: '_build/css/',
                src: '*.css',
                dest: '_build/css/'
            }
        },
    });

grunt.registerTask('build', [
        'clean:build',
        'handlebars',
        'compass',
        'autoprefixer',
        'copy:build',
        'useminPrepare',
        'concat',
        'uglify',
        'cssmin',
        'clean:jsFolders',
        'rev',
        'usemin',
    ]);

};

UPDATE

Tried @Andy's solution, it still shows the same error "Destination (_build/js/app.js) not written because src files were empty." and it also says below while building

 uglify:
  { options:
   { sourceMap: true,
     sourceMapName: '_build/js/app.js.map' },
  js: { files: { '_build/js/app.js': [ '_build/js/app.js' ] } },
  generated:
   { files:
      [ { dest: 'dist\\js\\app.js',
          src: [ '.tmp\\concat\\js\\app.js' ] } ] } }

Don't know where it got dest name from. My output folder is _build.

UPDATE2:
Refer to below links for better solution
http://stackoverflow.com/a/20574196/148271 https://github.com/gruntjs/grunt-contrib-uglify/issues/39#issuecomment-14856100