js相关方法的polyfill

assign

if(typeof Object.assign != 'function'){
  Object.assign = function(target){
    'use strict';
    if(target == null){
      throw new TypeError('Cannot convert undefined or null to object');
    }
    target = Object(target);
    for(var index = 1, len = arguments.length; index < len; index++){
      var source = arguments[index];
      if(source != null){
        for(var key in source){
          if(Object.prototype.hasOwnProperty.call(source, key)){
            target[key] = source[key];
          }
        }
      }
    }
    return target;
  }
}

create

if (typeof Object.create !== "function") {
  Object.create = function (proto, propertiesObject) {
    if (!(proto === null || typeof proto === "object" || typeof proto === "function")) {
       throw TypeError('Argument must be an object, or null');
     }
     var temp = new Object();
     temp.__proto__ = proto;
     if(typeof propertiesObject ==="object"){
       Object.defineProperties(temp,propertiesObject);
     }
     return temp;
  }
}

deepFreeze

function deepFreeze(obj){
  var o, key;
  Object.freeze(obj);
  for(key in obj){
    o = obj[key];
    if( !(o.hasOwnProperty(key)) || !(typeof o === 'object') || Object.isFreeze( o ) ){
      continue;
    }
    deepFreeze(o);
  }
}

is

if(typeof Object.js !== 'function'){
  Object.is = function (x, y){
    if(x === y){
      // +0 != -0
      return x !== 0 || 1/x !== 1/y;
    }else{
      // NaN == NaN
      return x !== x && y !== y;
    }
  }
}