Javascript IOS5"JavaScript执行超出超时"

Question

以下测试基本上是〜1000次数学运算,并且在大多数PC和Android浏览器以及iOS 4.x上运行良好.在iOS5 safari(iPhone 4和iPad 2)上,我们得到"JavaScript:错误未定义JavaScript执行超出超时".任何帮助非常感谢谢谢.

/** Converts numeric degrees to radians */
if (typeof (Number.prototype.toRad) === "undefined") {
    Number.prototype.toRad = function () {
    return this * Math.PI / 180;
    }
}

function gc(lat1, lon1, lat2, lon2) {
    // returns the distance in km between a pair of latitude and longitudes
    var R = 6371; // km
    var dLat = (lat2 - lat1).toRad();
    var dLon = (lon2 - lon1).toRad();
    var a = Math.sin(dLat / 2) * Math.sin(dLat / 2) +
        Math.cos(lat1.toRad()) * Math.cos(lat2.toRad()) *
        Math.sin(dLon / 2) * Math.sin(dLon / 2);
    var c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1 - a));
    var d = R * c;
    return d;
}

function test() {
    var d1 = new Date();
    var lat1, lon1, lat2, lon2;
    lat1 = -36;
    lon1 = 174;

    lat2 = lat1;
    lon2 = lon1;

    while (lat2 > -37) {
    lat2 = lat2 - 0.001;
    var stest = "lat1=" + lat1 + ",lon1=" + lon1 + ",lat2=" + lat2 + ",lon2=" + lon2 + "=" + gc(lat1, lon1, lat2, lon2);

    }
    var d2 = new Date();
    var stest = (d2.getTime() - d1.getTime()) / 1000.0 + "s";
    $("#lblTest").html(stest + "<BR/>" + $("#lblTest").html());

}

Answer 1

如果你想在javascript中执行一个长时间运行的操作,而你正在接近某些浏览器强制执行的脚本执行时间限制,那么你将不得不将你的功能分成多个部分,运行一个部分,到很短的时间setTimeout(fn, 1)然后执行下一个部分等...以这种方式执行,您可以运行代码数小时,因为它为其他脚本和其他事件提供了处理的机会.它有时需要少量的代码重构才能做到这一点,但总是可以做一点工作.

伪代码的基本概念是这样的:

var state = {};   // set initial state
var done = false;

function doWork() {
   // do one increment of work that will never get even close to the browser
   // execution time limit
   // update the state object with our current operating state for the next execution
   // set done = true when we're done processing
   if (!done) {
       setTimeout(doWork, 1);
   }
}

doWork();

在您的特定代码中,您可以执行类似的操作.您可以一次处理100个纬度点,然后执行短的setTimeout以执行下一个100,依此类推.您可以将该100个数字调整为最适合的数字.数字越大,您在每个计时器上执行的操作越多,总体执行时间越长,但您越接近浏览器脚本执行限制.setTimeout使浏览器保持活动状态(处理其他事件)并阻止执行时间限制.

function test() {
    var d1 = new Date();
    var lat1, lon1, lat2, lon2, done = false;;
    lat1 = -36;
    lon1 = 174;

    lat2 = lat1;
    lon2 = lon1;

    function calcGC() {
        var cntr = 0;
        while (lat2 > -37 && cntr < 100) {
            lat2 = lat2 - 0.001;
            var stest = "lat1=" + lat1 + ",lon1=" + lon1 + ",lat2=" + lat2 + ",lon2=" + lon2 + "=" + gc(lat1, lon1, lat2, lon2);
            cntr++;
        }
        // if we have more to go, then call it again on a timeout
        if (lat2 > -37) {
            setTimeout(calcGC, 1);
        } else {
            var d2 = new Date();
            var stest = (d2.getTime() - d1.getTime()) / 1000.0 + "s";
            $("#lblTest").html(stest + "<BR/>" + $("#lblTest").html());
        }
    }
    calcGC();
}