根据不存在的元素断开循环 [英] Break loop based on element not existing

问题描述

我建立了一个cms，允许用户在幻灯片中添加多达10个图像，这些图像都在前端以div的形式输出，并带有showcaseSlide，末尾添加0-9的数字。 showcaseSlide0，showcaseSlide1等。对于控制幻灯片显示的javascript，我需要将所有的div id输出到数组中，但在幻灯片播放结束时结束数组，例如，如果div id从showcaseSlide0 - showcaseSlide3中去掉了，我需要数组从幻灯片[0] - 幻灯片[3]。

下面是当前代码和一些我之前尝试过的注释过的代码：

  var slides = new Array（）; 
 var count = 0; 
 for（i = 0; i <= 10; i ++）{
 slides [i] =showcaseSlide+ i; 
 document.write（幻灯片[i]）; //这样我就可以看到数组中的哪个id 
 var div = document.getElementById（slides [i]）; 
 // if（div）{break; }<  - 不会中断
 //if（文档.getElementById (slides[i]）== null）break; <在第一个
之后的破坏//if（文档.getElementById（slides [i]）==未定义）break; <  - 在第一个
之后休息; 
  

编辑：

我已经发现（感谢Teemu下面评论）它没有工作，因为它在页面加载之前被调用，因此在对象被渲染之前被调用。我还要感谢Peter Kelly（他也在下面发表了评论），他指出我需要使用！在我的break语句中，Frazer指出我的循环太大了。

以下是新代码（包括初始化函数的其他元素）： p>

  var count = 0; 
 var wait = 4000; 
 var slides = []; 
 
函数startShowcase（）{
 
 for（var i = 0; i <10; i ++）{
 slides [i] =showcaseSlide+ i; ; 
 if（！document.getElementById（slides [i]））{break; } 
}; 
 setInterval（showcase，wait）; 
 
}; 
  

解决方案

您的DIV编号为0-9，但循环运行11次。

不是实际的代码，但是这可以解释它。

  for（i = 0; i <= 10; i ++）{
 0 = 1st 
 1 = 2nd 
 2 = 3rd 
 3 = 4th 
 4 = 5th 
 5 =第6个
 6 =第7个
 7 =第8个
 8 =第9个
 9 =第10个
 10 =第11个
} 
  

I have built a cms that allows users to add up to 10 images into the slideshow, which all output in the front end in divs with ids of showcaseSlide with a number from 0-9 appended on the end, e.g. showcaseSlide0, showcaseSlide1 etc. For the javascript that controls the slideshow, I need to output all of the div id's into an array, but end the array when the slides finish, eg if the div ids went from showcaseSlide0 - showcaseSlide3, I would need the array to go from slides[0] - slides[3].

Here is the current code and some commented out code that I have tried before:

var slides = new Array();
var count = 0;
for(i=0; i<=10; i++){
slides[i] = "showcaseSlide"+i;
document.write(slides[i]); //so that I can see which id's are in the array
var div = document.getElementById(slides[i]);
//if(div) { break; } <- doesn't break
//if(document.getElementById(slides[i]) == null) break; <-breaks after 1st
//if(document.getElementById(slides[i]) == undefined) break; <- breaks after 1st
};

Edit:

I've found out (thanks to Teemu who commented below) that it wasn't working because it was called before the page load, therefore before the objects were rendered. I also have to thank Peter Kelly (who also commented below), who pointed out that I needed to use a ! in my breaking if statement and Frazer who pointed out my loop was 1 too big.

Here is the new code (including the other elements of the initialising function):

var count = 0;
var wait = 4000;
var slides = [];

function startShowcase() {

    for(var i=0; i<10; i++){
        slides[i] = "showcaseSlide"+i;;
       if(!document.getElementById(slides[i])) { break; }
    };
    setInterval(showcase, wait);

};

解决方案

You have DIVs numbered 0-9 but your loop runs 11 times.

Not actual code, but this explains it.

for(i=0; i<=10; i++){
  0 = 1st 
  1 = 2nd
  2 = 3rd
  3 = 4th
  4 = 5th
  5 = 6th
  6 = 7th
  7 = 8th
  8 = 9th
  9 = 10th
  10 = 11th
}

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