这几道题，你会做吗？

1.考点：上下文

var a =1;var json = {    a:10,    val:function(){        alert(this.a*=2);    }}json.val();var b = json.val;b();alert("stop-stop")json.val.call(window);alert(window.a + json.a);

2.考点：属性

var a =1;var json = {    a:10,    val:function(){        alert(a*=2);    }}json.val();var b = json.val;b();alert("stop-stop")alert(window.a + json.a);

3.考点：原形链

function t1(name){ if(name) this.name  = name;}function t2(name){ this.name = name;}function t3(name){ this.name = name||"test";}t1.prototype.name = "yupeng";t2.prototype.name = "yupeng";t2.prototype.name = "yupeng";alert(new t1().name +new t2().name+new t3().name);

4.考点：闭包

var test = (function(a){    return function(){        alert(a*2);    }})(2);

test(20);