如何使用jQuery检查ID是否存在?

I want to have a line of code similar to below:

我想要一行代码如下所示:

var name = $('#input-name').attr("value");

However, the id 'input-name' is not guaranteed to exist. How do I check for its existence so that the assignment does not throw an error?

然而，id 'input-name'并不保证存在。如何检查它的存在性，使赋值不会抛出错误?

4 个解决方案

if ($('#input-name').length) {
  // do something
}

Check for .length or .size() on the object. The select won't fail, jQuery will always return an object.

检查对象上的.length或.size()。选择不会失败，jQuery将始终返回一个对象。

In my test the assignment didn't cause an error, it simply returned undefined.

在我的测试中，赋值没有导致错误，只是返回了未定义的值。

In which case the solution would be the following:

在这种情况下，解决办法如下:

var name = $('#input-name').attr("value");
if (name) {
  // blah blah
}

Or maybe:

或者:

var name = $('#input-name').attr("value") || 'defaultValue';

... if that makes sense in your case.

…如果这对你的情况有意义的话。

var name;
if ($('#input-name').length > 0)   
name= $('#input-name').attr("value");

if ($('#input-name').length) {
  // do something
}