一个极为简单的requirejs实现方法

//标记已经加载成功的个数
var REQ_TOTAL = 0;
//模块导出
window.exports = {};
//记录各个模块的顺序
var exp_arr = [];

//判断是否数组
function isArray(param) {
  return param instanceof Array;
}

//require 真正实现
function require(arr, callback) {

  var req_list;

  if(isArray(arr)) {
    req_list = arr;
  } else {
    req_list = [arr];
  }
  var req_len = req_list.length;

  //模块逐个加载
  for(var i=0;i<req_len;i++) {
    var req_item = req_list[i];

    var $script = createScript(req_item, i);

    var $node = document.querySelector('head');

    (function($script) {
      //检测script 的onload事件
      $script.onload = function() {
        REQ_TOTAL++;

        var script_index = $script.getAttribute('index');

        exp_arr[script_index] = exports;

        window.exports = {};

        //所有链接加载成功后，执行callback
        if(REQ_TOTAL == req_len) {
          callback && callback.apply(exports, exp_arr);

       
        }

      }

      $node.appendChild($script);
    })($script);

  }

}

//创建一个script标签
function createScript(src, index) {
  var $script = document.createElement('script');

  $script.setAttribute('src', src);
  $script.setAttribute('index', index);

  return $script;
}

exports.define = {
  topic: 'my export',
  desc: 'this is other way to define ',
  sayHello: function() {
    console.log('topic ' + this.topic + this.desc);
  }
}

exports.define = {
  name: 'xm',
  age: 22,
  info: function() {
    console.log('topic ' + this.name + this.age);
  }
}

//测试demo
 require(['../res/define.js', '../res/define2.js'], function(def, def2) {
   def.define.sayHello();
 
   def2.define.info();
 });