Module Code Splitting (--chunk / --module flag)

README.md

@@ -234,6 +234,38 @@ grunt.initConfig({
 });
 ```
 
+## Module Code Splitting
+
+Closure Compiler can split the output of a compilation into multiple files to support dynamic loading. This process uses the `--chunk` flag (before June 2018 it was named `--module`). See [how do I split my javascript into modules](https://stackoverflow.com/questions/10395810/how-do-i-split-my-javascript-into-modules-using-googles-closure-compiler/10401030#10401030)
+
+Modules can be stitched together without a module loading logic enabling to achieve optimal compression and optimization with the ability to load modules selectively.
+
+Source: https://github.com/google/closure-compiler/wiki/JS-Modules#code-splitting-output-modules
+
+```javascript
+grunt.initConfig({
+  'closure-compiler': {
+    frontend: {
+      closurePath: '/src/to/closure-compiler',
+      modules: {
+        "module-name": {
+          src: ['js/source.js', 'js/other-source.js']
+        },
+        "extra-module": {
+          src: ['js/extra-module.js'],
+          dep: ['module-name']
+        }
+      },
+      moduleOutputPath: 'static/js/',
+      maxBuffer: 500,
+      options: {
+        compilation_level: 'ADVANCED_OPTIMIZATIONS',
+        language_in: 'ECMASCRIPT5_STRICT'
+      }
+    }
+  }
+});
+```
 
 ## Note
 

tasks/closure-compiler.js

@@ -36,25 +36,34 @@ module.exports = function(grunt) {
     var command = 'java -jar "' + closurePath + '/build/compiler.jar"';
 
     data.cwd = data.cwd || './';
+
+    var output_mode;
+
+    // --module mode
+    if ("modules" in data) {
+      output_mode = 'modules';
+    } else { // --js mode
+      output_mode = 'js';
+
+      data.js = grunt.file.expand({cwd: data.cwd}, data.js);
+
+      // Sanitize options passed.
+      if (!data.js.length) {
+        // This task requires a minima an input file.
+        grunt.warn('Missing js property.');
+        return false;
+      }
 
-    data.js = grunt.file.expand({cwd: data.cwd}, data.js);
-
-    // Sanitize options passed.
-    if (!data.js.length) {
-      // This task requires a minima an input file.
-      grunt.warn('Missing js property.');
-      return false;
-    }
-
-    // Build command line.
-    command += ' --js "' + data.js.join('" --js "') + '"';
+      // Build command line.
+      command += ' --js "' + data.js.join('" --js "') + '"';
 
-    if (data.jsOutputFile) {
-      if (!grunt.file.isPathAbsolute(data.jsOutputFile)) {
-        data.jsOutputFile = path.resolve('./') + '/' + data.jsOutputFile;
+      if (data.jsOutputFile) {
+        if (!grunt.file.isPathAbsolute(data.jsOutputFile)) {
+          data.jsOutputFile = path.resolve('./') + '/' + data.jsOutputFile;
+        }
+        command += ' --js_output_file "' + data.jsOutputFile + '"';
+        reportFile = data.reportFile || data.jsOutputFile + '.report.txt';
       }
-      command += ' --js_output_file "' + data.jsOutputFile + '"';
-      reportFile = data.reportFile || data.jsOutputFile + '.report.txt';
     }
 
     if (data.externs) {
@@ -84,8 +93,34 @@ module.exports = function(grunt) {
       }
     }
 
-    // because closure compiler does not create dirs.
-    grunt.file.write(data.jsOutputFile, '');
+    if (output_mode === 'js') {
+      // because closure compiler does not create dirs.
+      grunt.file.write(data.jsOutputFile, '');
+    } else { // modules
+
+      for (var module in data.modules) {
+
+          // @todo add --define option for modules
+          //command += '" --define="DEBUG=false"';
+
+          data.modules[module].src.forEach(function(src) {
+              command += ' --js "' + src + '"';
+          });
+
+          command += ' --chunk "' + module + ':' + data.modules[module].src.length + ':';
+
+          // add dependency
+          if (data.modules[module].dep) {
+              command += data.modules[module].dep.join(',');
+              command += ':';
+          }
+          command += '"';
+      }
+
+      // module output directory
+      command += ' --module_output_path_prefix ' + data.moduleOutputPath;
+
+    }
 
     // Minify WebGraph class.
     exec(command, { maxBuffer: data.maxBuffer * 1024, cwd: data.cwd }, function(err, stdout, stderr) {