1、好奇怪的eval()函数

       
1、正常情况，eval()函数（它是全局对象的一个属性）用来解析一个表达式并计算的

       
2、奇怪问题一：字符串对象和字符串还是两个不一样的东西，eval()体现得最清楚

eval("2+2");    //4
eval(new String(2+2));      //2+2

       
3、奇怪问题二：eval()函数的引用直接变成全局调用

function test() {
  var x = 2, y = 4;
  console.log(eval('x + y'));    // Direct call, uses local scope, result is 6
  var geval = eval;     // equivalent to calling eval in the global scope
  console.log(geval('x + y'));  // Indirect call, uses global scope, throws ReferenceError because `x` is undefined
}

       
4、奇怪问题三：eval()解析字符串必须加()才能得出想要的结果

var jsonStr = "{a:20, b:10}";
console.log(eval('('+jsonStr+')'));     //{a: 20, b: 10}

       
5、奇怪问题四：她真的能计算

var zh_test = "你好";
var en_tesh = "hello";
var lang = "zh";
var language = lang+"_test";
console.log(language);      //“zh_test”

var zh_test = "你好";
var en_tesh = "hello";
var lang = "zh";
var language = lang+"_test";
console.log(eval(language));    //"你好"