使用setTimeout func。 ＆安培;随机函数。动画类元素

Question

我的调试技巧并没有帮助我弄清楚我在这里做错了什么。

我希望使用setTimeout函数在指定时间后为数组中的每个元素设置动画。

我没有收到任何错误，并且循环似乎运行得很好，但是，阵列中没有任何元素最终从原始位置移动到新位置。

function publicity()
{
// placing elements with class name 'cCameras' inside an array
var eCamerasArray = $(".cCameras").toArray();
// creating 2 arrays to hold left & top values of each element
var iLeftPosArray = [];
var iTopPosArray = [];
// loop to run through each element in array
for( var i = 0; i < eCamerasArray.length; i++)
{
    // timer variable set for each element to be used in setTimeout func.
    var timer = Math.floor (Math.random()*300) + 100;
    // setTimeout func. used to animate each element after a specified (timer) time
    window.setTimeout (function ()
    {
        iLeftPosArray[i] = Math.floor (Math.random() *139) + 360;
        iTopPosArray[i] = Math.floor (Math.random() *160) + 100 ;
        $(eCamerasArray[i]).animate ({left: iLeftPosArray[i] + "px", top: iTopPosArray[i] + "px"}, 100, "linear");
        return [iLeftPosArray[i], iTopPosArray[i]];
    }, timer);
}
}

Answer 1

你可以通过创建闭包来修复它：

(function publicity() {
    var eCamerasArray = $(".cCameras"),
        iLeftPosArray = [],
        iTopPosArray = [],
        timer;
    for(var i = 0; i < eCamerasArray.length; i += 1) {
        timer = Math.floor (Math.random() * 300) + 100;
        (function (i) {
            window.setTimeout (function () {
                iLeftPosArray[i] = Math.floor (Math.random() * 139) + 360;
                iTopPosArray[i] = Math.floor (Math.random() * 160) + 100 ;
                $(eCamerasArray[i]).animate ({left: iLeftPosArray[i] + "px", top: iTopPosArray[i] + "px"}, 300, "linear");
                return [iLeftPosArray[i], iTopPosArray[i]];
            }, timer);
        }(i));
    }
}());

您可以在此处查看效果：http://jsfiddle.net/zHUAt/2/

祝你好运！

Answer 2

展开一个简单的循环，你可以看到会发生什么：

var i = 0;

window.setTimeout( function(){
      //No local i so it must be outside
    console.log(i);

}, 1000 );

i++;

window.setTimeout( function(){
     //No local i so it must be outside
    console.log(i);

}, 1000 );

i++;

window.setTimeout( function(){
      //No local i so it must be outside
    console.log(i);

}, 1000 );

如您所见，所有函数都引用相同的i，所以 一旦定时器触发，它们都会记录2。他们都不是 拥有本地i。

您可以像这样创建“本地”i：

(function(i){
|---------^  //i found here, no need to use the global i
|   window.setTimeout( function(){
-------------------- //no local i here so it must be outside
        console.log(i);

    }, 1000 );  


})(i) //pass the "global" i as argument, with the value it has right now