Question

下面是我的代码，当我将对象方法keydown添加到eventlistener时，我失去了对该对象的引用，任何人都知道为什么会发生这种情况？什么是正确的做法

<html>
<head>
<title>Testpage</title>

<script type="text/javascript"> 
Person = function(fname, lname)
    {
    this.lastname=fname;
    this.firstname=lname;
    }

Person.prototype.toString = function()
    {
    return this.firstname+" "+this.lastname;
    }

Person.prototype.keydown = function (event) 
    {
    alert(this.firstname);
    //return this.firstname+" "+this.lastname;
    }

function init() 
    {
    var k=new Person("Paul", "Nistor");
    document.getElementById("nowpressed").value=k.toString();

    window.addEventListener("keydown", k.keydown, true);
    }
</script>
</head>
<body onLoad="init();">
<form>
    Now pressed: <input id="nowpressed" name="nowpressed" type="text" size="20" value="">
</form>
</body>
</html>

Answer 1

一种方法是提供匿名功能：

window.addEventListener("keydown", function() {
    k.keydown();
}, true);

另一种方法是将k.keydown方法明确地绑定到适当的上下文：

window.addEventListener("keydown", k.keydown.bind(k), true);

添加侦听器时JavaScript失去引用

1 个答案: