1 files changed, 91 insertions, 0 deletions
diff --git a/app/assets/javascripts/dispatcher.js.es6 b/app/assets/javascripts/dispatcher.js.es6
new file mode 100644
index 00000000000..bce23e5b257
--- /dev/null
+++ b/app/assets/javascripts/dispatcher.js.es6
@@ -0,0 +1,91 @@
+((global) => {
+  class Dispatcher {
+    constructor() {
+      this.registeredModules = [];
+      this.executedModules = [];
+      document.addEventListener('page:change', this.processModules.bind(this));
+      document.addEventListener('page:before-unload', this.processModules.bind(this));
+    }
+
+    /**
+     * Registers a module to a page query, or an array of page queries.
+     * Module page queries are matched against the `body` `date-page` attribute
+     * in order to
+     * @param {String} pageQuery - A page query, often taken from the body
+     *                           `data-page` attribute.
+     *                           e.g. `primary:secondary:tertiary`.
+     *                           It can also accept wildcards.
+     *                           e.g. `primary:*:tertiary`.
+     * @param {Function} module - A function to be invoked when a module's
+     *                          page query matches the current page identifier.
+     * @return {Undefined}
+     */
+    register(pageQuery, module) {
+      if (_.isArray(pageQuery)) {
+        for (pageQuery of pageQuery) {
+          this.registerModule(pageQuery, module);
+        }
+      } else {
+        this.registerModule(pageQuery, module);
+      }
+    }
+
+    processModules(e) {
+      const shouldDestroy = (e.type === 'page:before-unload');
+      for (let i = 0; i < this.registeredModules.length; i++) {
+        const module = this.registeredModules[i];
+        if (shouldDestroy) {
+          this.destroyModule(module);
+        } else {
+          this.executeModule(module);
+        };
+      }
+      if (shouldDestroy) this.executedModules = [];
+    }
+
+    registerModule(pageQuery, module) {
+      this.registeredModules.push({
+        pageQuery,
+        module,
+      });
+    }
+
+    destroyModule(module) {
+      if (!module.destroyableInstance) return;
+      if (module.destroyableInstance.destroy) module.destroyableInstance.destroy();
+      delete module.destroyableInstance;
+      delete global[module.module.name];
+    }
+
+    executeModule(module) {
+      if (!this.isExecutable(module)) return;
+      try {
+        module.destroyableInstance = new module.module();
+      } catch (e) {
+        module.destroyableInstance = module.module();
+      }
+      global[module.module.name] = module.module;
+      this.executedModules.push(module.module.name);
+    }
+
+    isExecutable(module) {
+      for (let i = 0; i < this.executedModules.length; i++) {
+        const executedModuleName = this.executedModules[i];
+        if (module.module.name === executedModuleName) {
+          return false;
+        }
+      }
+      return this.matchesPageIdentifier(module)
+    }
+
+    matchesPageIdentifier(module) {
+      const currentPageIdentifier = document.body.attributes['data-page'].value;
+      const pageQueryRegexString = module.pageQuery.replace(/\*/g, '.*');
+      const pageQueryRegex = new RegExp(pageQueryRegexString, 'gi');
+      return pageQueryRegex.test(currentPageIdentifier);
+    }
+  }
+
+  global.Dispatcher = new Dispatcher();
+
+})(window.gl || (window.gl = {}));