汇盛国际:你真的了解JavaScript吗?

标签:新闻动态    日期:2018-01-29 09:49    录入:汇盛国际平台    浏览:

  

[你真的了解JavaScript吗]你真的了解JavaScript吗?

  说出它们的值  
  
1、typeof(NaN) 、typeof(Infinity)、typeof(null)、typeof(undefined)  
2、NaN == NaN  
3、NaN != NaN  
4、NaN >= NaN  
5、null == undefined  
6、null >= undefined  
7、null <= undefined  
8、parseInt("123abc")  
9、"123abc" - 0  
10、Infinity > 10  
11、Infinity > "abc"  
12、Infinity == NaN  
13、true == 1  
14、new String("abc") == "abc"  
15、new String("abc") === "abc"  
  
说出它们的输出结果  
  
1、  
var a = "123abc";  
alert(typeof(a++));  
alert(a);  
  
2、  
var a = "123abc";  
a.valueOf = function(){return parseInt(a);}  
alert(++a);  
alert(a-0);  
  
3、  
var a = new Object();  
a.toString = function(){return "123abc";}  
a.valueOf = function(){return parseInt(a);}  
alert(++a);  
alert(a-0);  
  
4、  
String.prototype.valueOf = function()  
{  
return parseFloat(this);  
}  
alert("123abc" > 122);  
alert(new String("123abc") > 122);  
  
5、  
var s = new String("abc");  
alert(typeof(s) == typeof("abc"));  
alert(s === "abc");  
alert(s.toString() == s);  
  
6、  
var a = new Object();  
a.toString = function(){return "a"};  
var b = new Object();  
b.toString = function(){return "b"};  
alert(a>b);  
a.valueOf = function(){return 1};  
b.valueOf = function(){return 0};  
alert(a>b);  
  
7、  
function step(a)  
{  
return function(x)  
{  
return x + a++;  
}  
}  
var a = step(10);  
var b = step(20);  
alert(a(10));  
alert(b(10));  

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