es5标准-9.12 The SameValue Algorithm-实现

9.12 The SameValue Algorithm链接描述

9.12 The SameValue Algorithm
The internal comparison abstract operation SameValue(x, y), where x and y are ECMAScript language values, produces true or false. Such a comparison is performed as follows:

1.If Type(x) is different from Type(y), return false.
2.If Type(x) is Undefined, return true.
3.If Type(x) is Null, return true.
4.If Type(x) is Number, then.

a.If x is NaN and y is NaN, return true.
b.If x is +0 and y is -0, return false.
c.If x is -0 and y is +0, return false.
d.If x is the same Number value as y, return true.
e.Return false.

5.If Type(x) is String, then return true if x and y are exactly the same sequence of characters (same length and same characters in corresponding positions); otherwise, return false.
6.If Type(x) is Boolean, return true if x and y are both true or both false; otherwise, return false.
7.Return true if x and y refer to the same object. Otherwise, return false.

function SameValue (a,b){
  // Number.isNaN=Number.isNaN||function (a){return typeof a==='number'&&isNaN(a);}; 
   if (typeof a !== typeof b) {
       //类型不同
        return false;
   } else if (typeof a === 'undefined') {
       //类型相同都为undfined
        return true;
   } else if (typeof a === 'object'){
       //object有三种Array,{},null
       if (a === null && b === null) {
           //同为null
            return true;
       } else if (Array.isArray(a) && Array.isArray(b)){
           //同为array
           var alength = a.length,
                blength = b.length;
            if (alength === blength){
                for (var i = 0; i < alength; i++) {
                    if (!SameValue(a[i], b[i])) {
                        return false;
                    }
                }
                return true;
            } else {
                return false;
            }
       }else if (a !== null && !Array.isArray(a) && b !==null && !Array.isArray(b)){
            //处理都为object时
            return true;
       }else{
           //虽都为object,但不同null或array或{}
            return false;
       }
   } else if (typeof a === 'number') {
       //number有三种NaN,0,+-infinity不考虑
        if (isNaN(a) && isNaN(b)){
            return true;
        }else if (a === b){
            return true;
        }else{
            return false;
        }
   }else if (a.toString() === b.toString()){
       //其他情况剩余function
        return true;
   }else{
        return false;
   }
}

暂时未实现第4条的b,c..以及{}相等的解析未做。。