Usage Examples

Concatenating with a custom separator

In this example, running grunt concat:dist (or grunt concat because concat is a [multi task][]) will concatenate the three specified source files (in order), joining files with ; and writing the output to dist/built.js.

// Project configuration.
grunt.initConfig({
  concat: {
    options: {
      separator: ';'
    },
    dist: {
      src: ['src/intro.js', 'src/project.js', 'src/outro.js'],
      dest: 'dist/built.js'
    }
  }
});

Banner comments

In this example, running grunt concat:dist will first strip any preexisting banner comment from the src/project.js file, then concatenate the result with a newly-generated banner comment, writing the output to dist/built.js.

This generated banner will be the contents of the banner template string interpolated with the config object. In this case, those properties are the values imported from the package.json file (which are available via the pkg config property) plus today's date.

Note: you don't have to use an external JSON file. It's also valid to create the pkg object inline in the config. That being said, if you already have a JSON file, you might as well reference it.

// Project configuration.
grunt.initConfig({
  pkg: grunt.file.readJSON('package.json'),
  concat: {
    options: {
      stripBanners: true,
      banner: '/*! <%= pkg.name %> - v<%= pkg.version %> - ' +
        '<%= grunt.template.today("yyyy-mm-dd") %> */'
    },
    dist: {
      src: ['src/project.js'],
      dest: 'dist/built.js'
    }
  }
});

Multiple targets

In this example, running grunt concat will build two separate files. One "basic" version, with the main file essentially just copied to dist/basic.js, and another "with_extras" concatenated version written to dist/with_extras.js.

While each concat target can be built individually by running grunt concat:basic or grunt concat:extras, running grunt concat will build all concat targets. This is because concat is a [multi task][].

// Project configuration.
grunt.initConfig({
  concat: {
    basic: {
      src: ['src/main.js'],
      dest: 'dist/basic.js'
    },
    extras: {
      src: ['src/main.js', 'src/extras.js'],
      dest: 'dist/with_extras.js'
    }
  }
});

Multiple files per target

Like the previous example, in this example running grunt concat will build two separate files. One "basic" version, with the main file essentially just copied to dist/basic.js, and another "with_extras" concatenated version written to dist/with_extras.js.

This example differs in that both files are built under the same target.

Using the files object, you can have list any number of source-destination pairs.

// Project configuration.
grunt.initConfig({
  concat: {
    basic_and_extras: {
      files: {
        'dist/basic.js': ['src/main.js'],
        'dist/with_extras.js': ['src/main.js', 'src/extras.js']
      }
    }
  }
});

Dynamic filenames

Filenames can be generated dynamically by using <%= %> delimited underscore templates as filenames.

In this example, running grunt concat:dist generates a destination file whose name is generated from the name and version properties of the referenced package.json file (via the pkg config property).

// Project configuration.
grunt.initConfig({
  pkg: grunt.file.readJSON('package.json'),
  concat: {
    dist: {
      src: ['src/main.js'],
      dest: 'dist/<%= pkg.name %>-<%= pkg.version %>.js'
    }
  }
});

Advanced dynamic filenames

In this more involved example, running grunt concat will build two separate files (because concat is a [multi task][]). The destination file paths will be expanded dynamically based on the specified templates, recursively if necessary.

For example, if the package.json file contained {"name": "awesome", "version": "1.0.0"}, the files dist/awesome/1.0.0/basic.js and dist/awesome/1.0.0/with_extras.js would be generated.

// Project configuration.
grunt.initConfig({
  pkg: grunt.file.readJSON('package.json'),
  dirs: {
    src: 'src/files',
    dest: 'dist/<%= pkg.name %>/<%= pkg.version %>'
  },
  concat: {
    basic: {
      src: ['<%= dirs.src %>/main.js'],
      dest: '<%= dirs.dest %>/basic.js'
    },
    extras: {
      src: ['<%= dirs.src %>/main.js', '<%= dirs.src %>/extras.js'],
      dest: '<%= dirs.dest %>/with_extras.js'
    }
  }
});

Invalid or Missing Files Warning

If you would like the concat task to warn if a given file is missing or invalid be sure to set nonull to true:

grunt.initConfig({
  concat: {
    missing: {
      src: ['src/invalid_or_missing_file'],
      dest: 'compiled.js',
      nonull: true,
    },
  },
});

See configuring files for a task for how to configure file globbing in Grunt.

Custom process function

If you would like to do any custom processing before concatenating, use a custom process function:

runt.initConfig({
  concat: {
    dist: {
      options: {
        // Replace all 'use strict' statements in the code with a single one at the top
        banner: "'use strict';\n",
        process: function(src, filepath) {
          return '// Source: ' + filepath + '\n' +
            src.replace(/(^|\n)[ \t]*('use strict'|"use strict");?\s*/g, '$1');
        },
      },
      files: {
        'dist/built.js': ['src/project.js'],
      },
    },
  },
});