While loop within Javascript function

Question

I have the following basic function:

<script type="text/javascript">
function Form_Data(theForm)
{

var t=1;
while (t<=5) {

if (theForm.F[t]FirstName.value == "")
    {
    alert("Please enter Fighter 1's First Name.");
    theForm.F[t]FirstName.focus();
    return (false);
    }
t++;
}

return (true);
}
</script>

The script (js validation) fails using this code. If I remove the [t] and replace with a number (1,2,3,4,etc), the validation works on the appropriate fields. What am I doing wrong?

Note that the parentheses in return statements are not necessary :) — Matchu
– Matchu, Commented May 26, 2010 at 22:26
What exactly are you trying to do? F[t]FirstName looks to me like invalid syntax. — Matchu
– Matchu, Commented May 26, 2010 at 22:27
@Matchu - thank you for iterating my question/point. I have errors so something is not right with the code. As I state at the end, if I replace the variable with a number I get my validation. I have over 20 IF statements and up to 16 different 't' values — JM4
– JM4, Commented May 26, 2010 at 22:31
@JM4 - Are you replacing the t with a number or are you replacing [t] with a number? Please post a snippet of the code that works. We don't know what your object model looks like. — Eric Mickelsen
– Eric Mickelsen, Commented May 26, 2010 at 22:32
@tehMick - [t] with a number so the end result would look like: theForm.F3FirstName.value — JM4
– JM4, Commented May 26, 2010 at 22:33

Matchu · Accepted Answer · 2010-05-26 22:35:40Z

3

You can't use an index as part of a name, you have to put the name together as a string and use as index:

theForm['F' + t + 'FirstName']

edited May 26, 2010 at 22:35

Matchu

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answered May 26, 2010 at 22:28

Guffa

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10 Comments

Eric Mickelsen Over a year ago

You don't need both the dot and the brackets.

Matchu Over a year ago

@JM4 - I removed the syntax error. Looking at the comments, this is the solution to your problem :) Brackets represent accessing a property, not interpolating into a property name.

JM4 Over a year ago

@Matchu - no this is not, this solution does not work. I have tried it.

Matchu Over a year ago

@JM4 - Yeah. It is. Given the problem you describe, this is the solution. Please include a more complete code sample in the original question, because there must be an additional issue.

Matchu Over a year ago

@JM4 - Glad to help :P Just to give that answer a bit of explanation... If I have an object with the property foo, I can get to it with the easier syntax of obj.foo, or I can use obj[foo]. They are completely interchangable. You'll use the first more often, but the second allows you to include some more Javascript code inside the brackets, whereas the first will only take a straight-up, hard-coded property name. Hope that makes things a tad clearer :)

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