Question

我无法从另一个已在构造函数中实例化的函数访问JavaScript变量。它返回undefined。

我正在实例化类Box的新对象，并在构造函数中，定义实例变量，创建HTML元素和设置事件侦听器。此侦听器的处理程序clickHandler是在原型上定义的函数。从clickHandler开始，我正在尝试访问this.selected变量。但我得到undefined。

代码：

HTML

<!DOCTYPE html>
<html>
<head>  

<title>Test</title>
</head>
<body>

<div id="element1"></div>
<br/>
<div id="element2"></div>  

<script type="text/javascript" src="script.js"></script>
<script>
    init([{id: "element1"}, {id: "element2"}]); //call init function
</script>

</body>
</html>

Javascript script.js

function Box(id, count) { //the class
    this.selected = false; //need this variable in clickHandler
    this.div = document.createElement("div");
    this.div.id = "container" + count;
    this.div.style.width = "250px";
    this.div.style.height = "150px";
    this.div.style.border = "1px solid black";
    document.getElementById(id).appendChild(this.div);
    this.div.addEventListener("click", this.clickHandler, false); //add event listener on the created div element
}

Box.prototype.clickHandler = function() { //click handler
    console.log("clickHandler, selected = " + this.selected); // undefined
};

function init(settings) {
    //var obj;
    for(var i = 0; i < settings.length; i++) {
        new Box(settings[i].id, (i+1)); //instantiate new object
    }
}

如何在各种事件处理函数中访问this.selected变量？我计划监听多个事件，并需要this.selected变量。谢谢你的帮助。

Answer 1

将处理程序添加到：

this.div.addEventListener("click", this.clickHandler.bind(this), false);

这会将对象绑定为回调函数中的“this”上下文。

function Box(id, count) { //the class
    this.selected = false; //need this variable in clickHandler
    this.div = document.createElement("div");
    this.div.id = "container" + count;
    this.div.style.width = "250px";
    this.div.style.height = "150px";
    this.div.style.border = "1px solid black";
    document.getElementById(id).appendChild(this.div);
    this.div.addEventListener("click", this.clickHandler.bind(this), false);
}

Box.prototype.clickHandler = function() { //click handler
    console.log("clickHandler, selected = " + this.selected); // undefined
};

function init(settings) {
    //var obj;
    for(var i = 0; i < settings.length; i++) {
        new Box(settings[i].id, (i+1)); //instantiate new object
    }
}
    init([{id: "element1"}, {id: "element2"}]); //call init function

<div id="element1"></div>
<br/>
<div id="element2"></div>

从其他函数访问实例变量

1 个答案: