How can I tell between a blank textbox and a textbox with zero in it in JavaScript?

Question

I have the following:

var NewCount = document.getElementById('MainContent_gv_NewCount_' + rowIndex).value;
if (NewCount != "") {
    document.getElementById('MainContent_gv_lblTotal_' + rowIndex).innerHTML = "£" + ((originalCount - NewCount) * unitCost).toFixed(2);
} else { 
   document.getElementById('MainContent_gv_lblTotal_' + rowIndex).innerHTML = "";
            }

The calculations I am doing are based on the value in the textbox. (NewCount).

I want the label to update if the value is any number (including 0), but to be wiped if the user clears the textbox. However, at the moment it is treating a blank textbox and a textbox with 0 in it the same.

How can I differentiate between the two?

I don't believe that the code you posted could possibly be responsible for what you perceive to be going wrong. The comparison you've got, `NewCount != ""`, will be `true` when the value of the input box is any non-empty string, including the string "0". — Pointy, Feb 04 '11 at 13:48

score 3 · Accepted Answer · answered Feb 04 '11 at 13:44

3

Use !== in your if statement.

answered Feb 04 '11 at 13:44

Daniel A. White

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But `"0" != ""` evaluates (as one would expect) to `true`. – Pointy Feb 04 '11 at 13:47
why? can you provide a link or an explanation? – Shawn Mclean Feb 04 '11 at 14:56
@Shawn - http://stackoverflow.com/questions/1995113/strangest-language-feature/1998224#1998224 – Daniel A. White Feb 04 '11 at 16:27

score 1 · Answer 2 · answered Feb 04 '11 at 13:53

1

I can't reproduce the behavior you are describing. In my tests a textbox with "0" in it will be considered not blank by Javascript using your comparison logic (!= "").

Here is my attempt: http://jsfiddle.net/pJgyu/5404/

answered Feb 04 '11 at 13:53

joshuapoehls

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Šime Vidas · Answer 3 · 2011-02-04T14:00:56.223

0

if ( NewCount.length == 0 ) {
    // text-box is empty
} else if ( !isNaN(NewCount) ) {
    // the value is a number
}

edited Feb 04 '11 at 14:00

answered Feb 04 '11 at 13:44

Šime Vidas

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score 0 · Answer 4 · answered Feb 04 '11 at 13:46

0

Any of the following could work

NewCount.length > 0
NewCount !== ''

answered Feb 04 '11 at 13:46

Nalum

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How can I tell between a blank textbox and a textbox with zero in it in JavaScript?

4 Answers4