requireModule and addModule

requireModule can be used for Meta-Modules to prevent duplicate requires

lib/module.js

@@ -10,6 +10,7 @@ class Module {
   constructor (nuxt) {
     this.nuxt = nuxt
     this.options = nuxt.options
+    this.modules = []
   }
 
   addVendor (vendor) {
@@ -75,7 +76,14 @@ class Module {
     this.options.router.extendRoutes = chainFn(this.options.router.extendRoutes, fn)
   }
 
-  installModule (moduleOpts) {
+  requireModule (moduleOpts) {
+    if (this.modules.indexOf(moduleOpts) !== -1 || this.modules.indexOf(moduleOpts.src) !== -1) {
+      return
+    }
+    this.addModule(moduleOpts)
+  }
+
+  addModule (moduleOpts) {
     /* istanbul ignore if */
     if (!moduleOpts) {
       return
@@ -107,6 +115,8 @@ class Module {
       // eslint-disable-next-line no-console
       console.error('[Nuxt] Module should be a function', module)
     }
+    // Add module to this.modules
+    this.modules.push(module)
     // Call module with `this` context and pass options
     return new Promise((resolve, reject) => {
       const result = module.call(this, options, err => {

lib/nuxt.js

@@ -118,7 +118,7 @@ class Nuxt {
     // Add module integration
     this.module = new Module(this)
     // Install all modules in sequence and then return `this` instance
-    return utils.sequence(options.modules, this.module.installModule.bind(this.module))
+    return utils.sequence(options.modules, this.module.addModule.bind(this.module))
       .then(() => this)
       .catch(/* istanbul ignore next */ (err) => {
         console.error('[nuxt] error while initializing modules') // eslint-disable-line no-console