Javascript document.getElementByID（…）为NULL

Question

i got a problem in Javascript. i want to set a value from text input to a specific value, when clicking a link.

<form method="get" action="db.php">
<dl>
    <dt>
        Part:
    </dt>
    <dd>
        <input type="text" name="part"></input>
    </dd>
....
....  
<a href="#" onClick="document.getElementById('part').value = 'motor';">motor</a>   

but the

TypeError: document.getElementById(...) is null    

error appear

whats wrong with it?

Answer 1

getElementById find an element by id . There is no elementi with id = part in your dom sample. That's why it returns null. You could use document.getElementsByName(string) and it would return the array with the elemtns with the name specified, in your could, the 0 index get the input tag!

<a href="#" onClick="document.getElementsByName('part')[0].value = 'motor';">motor</a> 

It will return and array , so get the first element. Would be nice if you check it on a function if you get some result and apply the value property.

Answer 2

只需将id添加到输入标签，然后就可以使用getElementById（'part'）

<input type="text" name="part" id="part"></input>

Answer 3

Your <a> has a NAME of "part", not an ID. Therefor, there is no element on the page with an ID of "part", which is why you get a null result.