javascript - settimeout 调用的函数未结束

Question

问题:在幻灯片放映中，下面的淡入淡出函数不断调用淡入/淡出函数，请使用 JsFiddle 并运行大约十秒来查看问题。在 IE 中不起作用，不要让 jsfiddle 运行太久，它可能会使您的浏览器崩溃!

JsFiddle:http://jsfiddle.net/HdYmH/

详细信息(对于那些感兴趣的人):嗨，很抱歉发布一个包含如此大代码块的问题。我仍在学习 javascript，并试图弄清楚如何制作幻灯片。我知道有很多 js 幻灯片，但我想将其作为一种学习体验。因此请注意，这段代码的某些部分非常糟糕。该问题可能与幻灯片的changeSlide()方法有关。

我使用 firebug 来找出哪个方法被调用最多，显然几秒后 fadeOut 将被调用 20k+ 次:|

// Generic fade function that fades in or out
function fade(pElem, pStartOpac, pEndOpac, fps, sec) {
    if ((typeof (pElem) !== "string") || (typeof (pStartOpac) !== "number")
            || (typeof (pEndOpac) !== "number") || (typeof (fps) !== "number")
            || (typeof (sec) !== "number")) {
        console.log("Parameters incorrect format has to be (string) Element Id, (double) Starting Opacity, (double) End Opacity, (integer) frames per second, (integer) seconds to run");
        return;
    }
    // The CSS opacity property only works from 1 to 0
    if (pStartOpac < 0) {
        pStartOpace = 0;
    }
    if (pStartOpac > 1) {
        pStartOpac = 1;
    }
    if (pEndOpac < 0) {
        pEndOpac = 0;
    }
    if (pEndOpac > 1) {
        pEndOpac = 1;
    }

    // Stop the fps from going over 60 or under 1 (The eye will barely notice
    // improvements above 60fps and fractional fps are not supported)
    if (fps > 60) {
        fps = 60;
    }
    if (fps < 1) {
        fps = 1;
    }

    var totalFrames = (fps * sec);
    var opacityChangePerSecond = (Math.abs(pStartOpac - pEndOpac) / sec);
    var opacityChangePerFrame = (opacityChangePerSecond / fps);
    var timeOutInterval = 1000 * (1 / fps);

    // console.log("totalFrames: "+totalFrames);
    // console.log("Opacity change per second: " + opacityChangePerSecond);
    // console.log("Opacity change per frame: " + opacityChangePerFrame);
    // console.log("Time out interval: " + timeOutInterval + " milliseconds");

    var opacity = pStartOpac;
    var timeoutVar;
    var elemId = document.getElementById(pElem);
    elemId.style.opacity = opacity;

    if (pStartOpac < pEndOpac) {
        fadeIn();
        return;
    } else {
        fadeOut();
        return;
    }

    function fadeIn() {
        opacity = opacity + opacityChangePerFrame;
        if (opacity > pEndOpac) {
            clearTimeout(timeoutVar);
            return;
        }
        elemId.style.opacity = opacity;
        timeoutVar = setTimeout(fadeIn, timeOutInterval);
        return;
    }

    function fadeOut() {
        if (opacity < pEndOpac) {
            clearTimeout(timeoutVar);
            return;
        }
        opacity = opacity - opacityChangePerFrame;
        if (opacity < 0) {
            opacity = 0;
        }
        elemId.style.opacity = opacity;
        timeoutVar = setTimeout(fadeOut, timeOutInterval);
        return;
    }

}

Answer 1

遇到问题:当不透明度<0时，将其设置为0，然后执行:if (opacity < pEndOpac) 。 pEndOpac 为 0，因此 0<0 计算结果为 false，并且超时永远不会被清除。解决办法是if (opacity <= pEndOpac) :

function fadeIn() {
    opacity = opacity + opacityChangePerFrame;
    if (opacity >= pEndOpac) {
        clearTimeout(timeoutVar);
        return;
    }
    elemId.style.opacity = opacity;
    timeoutVar = setTimeout(fadeIn, timeOutInterval);
    return;
}

function fadeOut() {
    if (opacity <= pEndOpac) {
        clearTimeout(timeoutVar);
        return;
    }
    opacity = opacity - opacityChangePerFrame;
    if (opacity < 0) {
        opacity = 0;
    }
    elemId.style.opacity = opacity;
    timeoutVar = setTimeout(fadeOut, timeOutInterval);
    return;
}