如何创建一个JavaScript侦听器函数，当条件为true时将执行操作? [英] How do I create a javascript listener function that will perform an action when a condition is true?

问题描述

我正在使用第三方javascript，这使我非常需要侦听器.例如，当某个div已加载时，我想对其进行处理.它会同时改变对象的样式，因此我需要注意它是否具有某种样式.我已经建立了在存在ID或类时执行操作的函数.这是当前的ID功能.如您所见，它使用jQuery.

I'm using a third party javascript that has given me a lot of need for listeners. For instance, when a certain div has been loaded, I want to do something with it. It changes styles of objects as it goes as well so I need to watch for it to have a certain style. I've build functions to act when an id or class exists. Here's the current ID function. As you can see, it uses jQuery.

function whenLoaded(element_id, action) {
    if ($(element_id)) {
        action();
    }
    else {
        setTimeout("whenLoaded('"+element_ids+"',"+action+", '"+stop_on+"')", 500);
    }
}

我真的需要一些可以赋予多个条件的东西.例如:

I really need something that I can give multiple conditions to. For instance:

whenTrue(
    ($('popup') && $('popup').style.width == '500px'), 
    $('popup').style.width = '0'
);

我希望它可以递归检查条件(第一个参数).当这些条件成立时，请执行操作.

I would expect it to recursively check the conditions (1st param). When those conditions are true, perform the action.

我已经能够使用eval()完成此操作，但已警告我不要使用它，不记得为什么.话虽这么说，我想以另一种方式来做到这一点.

I've been able to accomplish this using eval() but I have been warned not to use it, can't remember why. That being said, I'd like to accomplish this in another way.

eval()解决方案:

eval() solution:

whenTrue(
    "($('popup') && $('popup').style.width == '500px')", 
    "$('popup').style.width = '0'"
);

function whenTrue(condition, action) {
    if (eval(condition)) {
        eval(action);
    }
    else {
        setTimeout("whenTrue('"+condition+"','"+action+"')", 500);
    }
}

推荐答案

function conditionListener(callback){
    if(typeof callback !== 'function') return;

    var interval, callback = callback;

    interval = setInterval(function() {
        if(true /* some condition */){
            callback();
            clearInterval(interval);
        }
    }, 500);
}

var listener = new conditionListener(function() {
    /* ... do work ... */
});

---

http://jsfiddle.net/M26XS/

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