Question

I’m trying to change the value of an input field with Javascript.
I tried everything, but nothing seems to works. I tried putting the 5 between quotation marks and using jquery. I also double-checked the array and everything.

Here is the input code:

<input type="number" id="id_[SOME_ID_HERE]" value="0">

and the loop used to update the values.

for (var i = 0; i < shoppingCart.length; i++) {
    var val = shoppingCart[i];
    document.getElementById("id_" + val.substring(3)).value = 5;
}

jsfiddle: http://jsfiddle.net/zkTud/

EDIT: Seems like it doesn’t work with type=”text” as well…

EDIT2: Thank you everyone who answered. My problem was actually something else.
The input was loaded from another page, and it took time and the for loop I had problem with (see above) was executed before the file was done loading.
All I did was to move the for loop as is to the callback function and it works now.

Thanks anyways!
I really appreciate the help I’m getting in this site! 🙂

Answer 1

The problem is that your call to substring is returning too much of the string, so there are no elements found by getElementById. Change it to this:

for(var i = 0; i < shoppingCart.length; i++) {
    var val = shoppingCart[i];
    document.getElementById("id_" + val.substring(5)).value = 5;
}

Here’s an updated fiddle.

The substring method (when called with one argument) returns the characters from the index specified to the end of the string. Since you are specifying index 3, you get “d_1”, “d_2” etc. when actually you just want the number.

Alternatively, you could of course change the string to which you append the substring, but I think that would be more confusing to read (not immediately obvious which element will be returned):

document.getElementById("i" + val.substring(3)).value = 5;