Macro substitution in Javascript

[andersond]

I have previously asked a question with the same title line but my situation and purpsse are different this time. I mean to be creating a function to go back over a form, identify blank required fields, change their borders to red then go back and give focus to the first one.

function checkUnitFields(x){
    var num=x; // item number
    var firstBlankField=null; // variable to be used to move focus to first field that needs attention
    var secondBlankField=null; // variable to be used to move focus to second field that needs attention
    var thirdBlankField=null; // variable to be used to move focus to third field that needs attention
    var fourthBlankField=null; // variable to be used to move focus to fourth field that need attention
    var fifthBlankField=null; // variable to be used to move focus to fifth field that needs attendtion
 
    if(isEmpty(document.getElementById('modelYear'+num).value)==true){
        document.getElementById('modelYear'+num).style.border="1px solid #FF0000";
        if(firstBlankField==null){
            firstBlankField="modelYear";
        }
    }
 
    if(isEmpty(firstBlankField)!=true){
        document.getElementById(firstBlankField).focus();
    }
 

There are actually five possible fields that could be blank but I only included the first here becauxe it has no problem identifying the blank fields and making the borders red. The problem is with the last if() statement where I am trying to return focus() to the first blank field. Since nothing is in parenthesis I am uncertain how to distinguish that I want the value of variable 'firstBlankField' substitued for the name of the variable in my getElementById() statement. Essentially I need to do a macro substitution and I don't know how. Can anybody offer a solution?

[acoder]

So you mean modelYear is the name of a variable?

You could improve this code and make it generic by looping over elements rather than using fixed variable names.

[andersond]

No. ModelYear is the name of the field. The variable is named firstBlankField. I want the macro to substitute 'modelYear' for 'firstBlankField' in the last if() statement. And so on.

I don't understand what you mean by 'looping over elements rather than using fixed variable names. How would I do that?

[acoder]

If modelYear was the ID, then your code would be correct. If it's the name, you could use the form elements collection:

document.forms[formName].elements[firstBlankField]...

By looping over the elements, I meant something like:

var len = document.forms[formName].elements.length;
for (...

or using document.getElementsByTagName("input") and then checking the type/name etc.

[Dormilich]

wasn't isEmpty() expecting an element as input?