javascript 未捕获的类型错误：无法读取未定义的属性“0”
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Uncaught TypeError: Cannot read property '0' of undefined
提问by MarcusJohnson
I've been banging my head against various inanimate objects for a while. I'm using jQuery to create a promotional banner rotation thing. Every 2 seconds (i'll change it to more in the future, just for testing it's short), the image and caption change.
一段时间以来，我一直在用头撞各种无生命的物体。我正在使用 jQuery 创建一个宣传横幅旋转的东西。每 2 秒（我将在未来将其更改为更多，只是为了测试它的短），图像和标题会发生变化。
This works fine, it rotates between them and when it gets to the last one, it goes back to the beginning. But when I click on one, and it goes back to the beginning (or I click on the first one explicitly), when it next tried to rotate it throws this:
这很好用，它在它们之间旋转，当它到达最后一个时，它又回到了开头。但是当我点击一个，它回到开头（或者我明确点击第一个），当它下一次尝试旋转时，它会抛出这个：
Uncaught TypeError: Cannot read property '0' of undefined /ftwc/:178
changeImage
rotate
On my two functions. I can't understand why!
关于我的两个功能。我不明白为什么！
Here is the script:
这是脚本：
changeImage = function(num) {
$(".currentpromoimage").before('<div class="promoimage newpromoimage" style="background: url(\''+images[num][0]+'\') no-repeat; z-index: 1;"><div class="caption" style="color: #'+images[num][2]+'">'+images[num][1]+'</div></div>');
$(".currentpromoimage").fadeOut(700,function(){
$(".newpromoimage").addClass("currentpromoimage");
$(".newpromoimage").removeClass("newpromoimage");
$(this).remove();
});
$(".newpromoimage").fadeIn(700);
$("#promoselect").children().children().css('background', '#303030');
$("#ps_"+num).css('background', '#000000');
currentImage = num;
};
rotate = function() {
var imageLength = images.length-1;
if (currentImage == imageLength) {
changeImage("0");
} else {
var nextImage = currentImage+1;
/*alert("nextImage:"+nextImage);*/
changeImage(nextImage);
}
};
var selectors = "";
var preloads = '';
for(var i=0;i<images.length;i++) {
preloads += '<img src="'+images[i][0]+'" alt="preloaded" class="preload">';
selectors += "<li id=\"ps_"+i+"\"></li>";
}
$("body").prepend(preloads);
$("#grass").after('<div id="promo"><div id="promoselect"><ul></ul></div><div class="promoimage currentpromoimage" style="background: url(\''+images[0][0]+'\') no-repeat; z-index: 1;"><div class="caption" style="color: #'+images[0][2]+'">'+images[0][1]+'</div></div></div>');
var currentImage = 0;
$("#promoselect").children().append(selectors);
$("#ps_0").css('background', '#000000');
$("#promoselect")
.children()
.children()
.click(function() {
var selector = $(this).attr("id").split("_");
clearInterval(autoimage);
changeImage(selector[1]);
autoimage = setInterval(rotate,2000);
});
autoimage = setInterval(rotate,2000);
This is all called inside the jQuery document ready function, and images is an array encoded from PHP using json_encode. I know it's messy at the moment but I just can't figure out why these functions are appearing undefined..
这一切都在 jQuery 文档就绪函数内部调用，图像是使用 json_encode 从 PHP 编码的数组。我知道目前它很混乱，但我无法弄清楚为什么这些函数显示为未定义..
Thanks!
谢谢！
回答by Bergi
You're using the imagevariable a lot, but don't define it anywhere (or wrong). Right in the first line, images[num]will evaluate to undefined, throwing an error when accessing images[num][0].
您经常使用该image变量，但不要在任何地方（或错误）定义它。就在第一行，images[num]将评估为undefined，在访问时抛出错误images[num][0]。
