几道题

1. 下面代码alert的内容

function tr42(){var a2, b2;a2 = {"c": 1};b2 = a2;a2.c = 2;alert(b2.c);     a2 = {"c": 3};alert(b2.c);     a2.c = 4;alert(b2.c);     
}
tr42();

2. 下面代码alert的内容

function tc51(){var a2 = 6;window.setTimeout((function(){alert(a2); a2 = 666;}), 1000);a2 = 66;window.setTimeout((function(){alert(a2);  }), 3000);
}
tc51();

3.请阐述 代码的功能,代码的优点和缺点. listener.apply(el)在此处的作用. 如果有可改进之处，请给出改进后的代码，并说明理由。

if (window.addEventListener) {var addListener = function(el, type, listener, useCapture){el.addEventListener(type, listener, useCapture);};
}
else if (document.all) {addListener = function(el, type, listener){el.attachEvent("on" + type, function(){listener.apply(el);});};
}

4. 下面代码alert的内容

function ts61(){try {i = 2;throw Error("error message!");} catch (err) {var i = 1;alert(err.message);}alert(i);alert(window.i);alert(window.err);alert(err.message);
}
ts61();

5. 最后三行 问号处分别可以填哪些值让表达式成立.

function to62(){function Person(name, age){this.name = name;this.age = age;this.getName = function(){alert(this.name);};}Person.prototype = {getAge: function(){alert(this.age);}};var p = new Person("bob", "21");P instanceof ? == truep.constructor == ?p.hasOwnProterty(?) == true
}
to62();

6. 简述如何各种浏览器内得到DomReady事件（写要点即可）