JavaScript 闭包

<form>
    <input id="text" type="text"/>
    <input id="btn" type="button" value="button"/>
</form>

<script>
document.getElementById("btn").onclick = function(){
    var value = document.getElementById("text").value;
    alert(value);
}
document.getElementById("btn").onclick = (function(){
    var input = document.getElementById("text");
    return function(){
        alert(input.value);
    }
})();

function A(){
    var name = "a";
    this.getName = function(){
        reutrn name;
    }
    this.setName = function(_name){
        name = _name;
    }
}
</script>

<script>
var fun = function(){
    var num = 0;
    return {
        call:function(){
            alert(num++);
        },
        reset:function(){
            num=0;
        }
    }
}();

var obj = {
        num:0,
        call:function(){
            alert(this.num++);
        },
        reset:function(){
            num=0;
        }
    };
obj.call();
alert(obj.num);
obj.reset();
alert(obj.num);

    
</script>