为什么这个 Javascript 方法不会继续调用自身？

发布于 2024-11-14 11:49:15 字数 548 浏览 3 评论 0原文

我有一个带有特权方法的 JavaScript 对象。当此方法完成后，我希望它调用自身（在短暂的超时后）并继续无限期地运行。不幸的是，该方法只运行两次，然后就停止了，没有任何错误（在 Chrome 和 IE 中测试，结果相同）。

代码如下：

function Test() {
    // ... private variables that testMethod needs to access ...
    this.testMethod = function() {
        alert("Hello, from the method.");
        setTimeout(this.testMethod, 2000);
    };
}

var myTest = new Test();
myTest.testMethod();

我希望每两秒收到一次警报，但它只显示警报两次，然后停止。您可以在此处查看实时示例。知道为什么会发生这种情况吗？

原文

I have a JavaScript object with a privileged method. When this method has completed, I would like it to call itself (after a small timeout) and continue running indefinitely. Unfortunately, the method only runs twice, then it stops without any error (tested in Chrome and IE with the same results).

The code is as follows:

function Test() {
    // ... private variables that testMethod needs to access ...
    this.testMethod = function() {
        alert("Hello, from the method.");
        setTimeout(this.testMethod, 2000);
    };
}

var myTest = new Test();
myTest.testMethod();

I would expect to get the alert every two seconds, but instead it only shows the alert twice, then stops. You can see a live example here. Any idea why this would be happening?

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如果没有 2024-11-21 11:49:15

因为函数外的this与函数内的this不一样。尝试改为：

function Test() {
    // ... private variables that testMethod needs to access ...
    var me = this;
    this.testMethod = function() {
        alert("Hello, from the method.");
        setTimeout(me.testMethod, 2000);
    };
}

Because this outside the function is not the same as this inside the function. Try instead:

function Test() {
    // ... private variables that testMethod needs to access ...
    var me = this;
    this.testMethod = function() {
        alert("Hello, from the method.");
        setTimeout(me.testMethod, 2000);
    };
}

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池木 2024-11-21 11:49:15

当您第一次使用“myTest.testMethod();”调用它时“this”关键字与“myTest”对象绑定，当超时触发时，“window”对象与“this”关键字绑定，并且“this.testMethod”相当于“window.testMethod”。
尝试：

function Test() {
    // ... private variables that testMethod needs to access ...
    this.testMethod = function() {
        alert("Hello, from the method.");
        setTimeout((function(self){
            return function(){self.testMethod();};
        })(this), 2000);
    };
}

var myTest = new Test();
myTest.testMethod();

或：

function Test() {
    // ... private variables that testMethod needs to access ...
    this.testMethod = function() {
        alert("Hello, from the method.");
        var self = this;
        setTimeout(function(){self.testMethod();}, 2000);
    };
}

var myTest = new Test();
myTest.testMethod();

When you first call it with "myTest.testMethod();" the "this" keyword is bond to your "myTest" object, when the timeout fires the "window" object is bond to "this" keyword and "this.testMethod" is equivalent to "window.testMethod".
Try:

function Test() {
    // ... private variables that testMethod needs to access ...
    this.testMethod = function() {
        alert("Hello, from the method.");
        setTimeout((function(self){
            return function(){self.testMethod();};
        })(this), 2000);
    };
}

var myTest = new Test();
myTest.testMethod();

Or:

function Test() {
    // ... private variables that testMethod needs to access ...
    this.testMethod = function() {
        alert("Hello, from the method.");
        var self = this;
        setTimeout(function(){self.testMethod();}, 2000);
    };
}

var myTest = new Test();
myTest.testMethod();

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葬﹪忆之殇 2024-11-21 11:49:15

尝试

function Test() {
    // ... private variables that testMethod needs to access ...
    this.testMethod = function() {
        alert("Hello, from the method.");
        var self = this;
        setTimeout(function() { self.testMethod(); }, 2000);
    };
}

或使用setInterval。

Try

function Test() {
    // ... private variables that testMethod needs to access ...
    this.testMethod = function() {
        alert("Hello, from the method.");
        var self = this;
        setTimeout(function() { self.testMethod(); }, 2000);
    };
}

or use setInterval.

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離人涙 2024-11-21 11:49:15

因为 setTimeout 中的 this 指的是本地函数 testMethod 而不是 Test ——本质上，你是在说 setTimeout( testMethod.测试方法，2000）

function Test() {
    // ... private variables that testMethod needs to access ...
    var self = this;
    self.testMethod = function() {
        alert("Hello, from the method.");
        setTimeout(self.testMethod, 2000);
    };
}

var myTest = new Test();
myTest.testMethod();

because the this in your setTimeout is referring to the local function testMethod not Test -- essentially, you are saying setTimeout( testMethod.testMethod, 2000 )

function Test() {
    // ... private variables that testMethod needs to access ...
    var self = this;
    self.testMethod = function() {
        alert("Hello, from the method.");
        setTimeout(self.testMethod, 2000);
    };
}

var myTest = new Test();
myTest.testMethod();

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