javascript 如何在 document.getElementById 中使用变量
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How do I use variables in document.getElementById
提问by user3052776
I have this code which I've been trying to fix for hours.
我有这个代码，我已经尝试修复了几个小时。
<script language="JavaScript">
<!--
function generate(){
var titels = new Array();
var i = 0;
for(i;i<9;i++){
var test = 'h1-0'+ i;
titels[i] = document.getElementById(test).textContent;
}
document.getElementById("uitkomst").value = titels[1];
}
-->
</script>
This gives me the error
这给了我错误
TypeError: document.getElementById(...) is null
titels[i] = document.getElementById(test).textContent;
But when I change 'h1-0'+i by 'h1-0'+5 it does work and I don't get an error, so how do I fix this? Why is Javascript so annoying when using variables?
但是，当我将 'h1-0'+i 更改为 'h1-0'+5 时它确实有效并且我没有收到错误消息，那么我该如何解决这个问题呢？为什么 Javascript 在使用变量时如此烦人？
回答by Pointy
Add another variable:
添加另一个变量：
var element;
and use it in the loop to hold on to the result of fetching (or trying to fetch) the element:
并在循环中使用它来保持获取（或尝试获取）元素的结果：
for (i; i < 9; i++) {
element = document.getElementById('h1-0' + i);
if (element) {
titles[i] = element.textContent;
}
else {
console.log("Element " + i + " not found.");
}
}
Then check the console to see which one is missing.
然后检查控制台以查看缺少哪个。
回答by jfriend00
There are a couple ways you can fix this issue - you can test for a missing object and skip that case or you can catch the exception that is thrown and act accordingly in the exception handler.
有几种方法可以解决此问题 - 您可以测试丢失的对象并跳过该情况，或者您可以捕获抛出的异常并在异常处理程序中采取相应的行动。
Here's how you could handle missing objects in your code:
以下是处理代码中丢失对象的方法：
function generate(){
var titels = [];
var i, item, test;
for (i = 0; i < 9; i++) {
test = 'h1-0'+ i;
item = document.getElementById(test);
if (item) {
titels[i] = item.textContent;
}
}
document.getElementById("uitkomst").value = titels[1];
}
If, this is really all your code is doing, then you don't need the forloop because you're only using the [1]item from the array and you can do this:
如果这真的是您的代码所做的全部，那么您不需要for循环，因为您只使用[1]数组中的项目，您可以这样做：
function generate() {
var item = document.getElementById("h1-01");
if (item) {
document.getElementById("uitkomst").value = item.textContent;
}
}
