避免使用requirejs加载已经注入DOM的模块

Question

有没有办法避免加载已存在于DOM中的模块？

例:

require.config({
  paths: {
    // jquery here is needed only if window.jQuery is undefined
    'jquery': '//ajax.googleapis.com/ajax/libs/jquery/1.10.2/jquery.min'
  }
});

能够使用这个片段之类的东西会很棒

require.config({
  paths: {
    'jquery': {
       uri: '//ajax.googleapis.com/ajax/libs/jquery/1.10.2/jquery.min',
       // if this function returns false or undefined load the script from the url
       define: function(){ return window.jQuery; } 
    }
  }
});

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UPDATE

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我和我的提议在github https://github.com/jrburke/requirejs/issues/886上向@jrburke发送了拉取请求.requirejs的固定版本可以在这里测试:

http://gianlucaguarini.com/experiments/requirejs/requirejs-test3.html

这里根据我的API提议配置requirejs

require.config({
  paths: {
    // jquery here is needed only if window.jQuery is undefined
    'jquery':'//ajax.googleapis.com/ajax/libs/jquery/1.10.2/jquery.min',
    'lodash':'//cdnjs.cloudflare.com/ajax/libs/lodash.js/2.0.0/lodash.underscore.min',
    'backbone':'//cdnjs.cloudflare.com/ajax/libs/backbone.js/1.0.0/backbone-min'
  },
  shim:{
    'jquery':{
      // with my fix now I detect whether window.jQuery has been already defined
      // in this case I avoid to load the script from the cdn
      exports:'jQuery',
      // if this feature is missing I need to load the new jQuery from the cdn
      validate: function(){
        return  window.jQuery.Defferred;
      }
    },
    'lodash':{
      // lodash will be loaded only if it does not exist in the DOM
      exports:'_',
      // if this function returns false or undefined load the script from the cdn
      validate: function() {
        // is the lodash version already available in the DOM new enough for my application?
        return  window.parseInt(window._.VERSION) >= 2;
      }
    },
    'backbone':{
      deps:['lodash','jquery'],
      // if backbone exists we don't need to load it twice
      exports:'Backbone'
    }
  }
});

Answer 1

由于 jQuery 与 AMD 兼容，如果它已经在页面中，Require.js 将不会再次加载它。

从更广泛的角度来说，Require.js 仅在模块尚未定义时才查看路径配置。因此，一旦定义了模块，Require.js 就不会再次加载它：

define('jquery', [], function() { /* stuff */ });
//        ^ Module 'jquery' is defined here. Require.js won't load it twice.

查看此 JsBin 以获取工作示例：http ://jsbin.com/OfIBAxA/2/edit