javascript not sure about the for loop syntax

Question

for (var i = 1; i < 100; i++) { 
if(document.FORM.chkTableType[i].checked==false && 
    document.FORM.chkTableType[i]+"_"+"1".checked==false &&
    document.FORM.chkTableType[i]+"_"+"2".checked==false )
    {
        window.alert("Please select at least 1 table to download");
        return false;
    }
}

I want to validate combo box in javascript, the purpose if having this document.FORM.chkTableType[i]+"_"+"1" is to generate something like the following:

document.FORM.chkTableType1_1

document.FORM.chkTableType1_2

document.FORM.chkTableType2_1

but it throws error: Unable to get property '1' of undefined or null reference

im not sure where whether the syntax of this is correct---> document.FORM.chkTableType[i]+"_"+"1"

yep, this is incorrect syntax document.FORM.chkTableType[i]+"_"+"1".checked — Grundy
– Grundy, Commented Nov 25, 2014 at 11:41
may i ask what should be the correct syntax? tried to google around but no luck. — hades
– hades, Commented Nov 25, 2014 at 11:44

Satinder singh · Accepted Answer · 2014-11-25 11:50:19Z

1

If I understand correctly, you're trying to build the property name dynamically like this.

for (var i = 1; i < 100; i++) { 
if(document.FORM['chkTableType' + i].checked==false && 
    document.FORM['chkTableType' + i + '_1'].checked==false &&
    document.FORM['chkTableType' + i + '_2'].checked==false )
    {
        window.alert("Please select at least 1 table to download");
        return false;
    }
}

edited Nov 25, 2014 at 11:50

Satinder singh

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answered Nov 25, 2014 at 11:44

Sam Greenhalgh

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1 Comment

Sam Greenhalgh Over a year ago

Incidentally, it might be a little cleaner to find the form using document.getElementById and use HTMLFormElement.elements to find the inputs. - developer.mozilla.org/en-US/docs/Web/API/…

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