How to test an empty input box?

chirs · Oct 17, 2003

I try to test a field to see if it's empty. But it prints "It is not
null". Why and how can I fix it?

<html>
<head>
</head>
<body>
<input type="text" name="box1">

<script>
if (box1.value != null) {document.write("It is not null")}
else {document.write("empty")}
</script>
</body>
</html>

Laurent Bugnion, GalaSoft · Oct 17, 2003

Hi,

I try to test a field to see if it's empty. But it prints "It is not
null". Why and how can I fix it?

<html>
<head>
</head>
<body>
<input type="text" name="box1">

<script>
if (box1.value != null) {document.write("It is not null")}
else {document.write("empty")}
</script>
</body>
</html>

null is the value that an object has when it hasn't been initialized, in
other word when no memory has been allocated for it yet.

The "value" property exists, however, even if it is empty. To test if a
field is empty, you must compare it to an empty string:

if ( document.formName.fieldName.value == "" )
{
//empty
}

Laurent

Jerry Park · Oct 17, 2003

Hi,

null is the value that an object has when it hasn't been initialized, in
other word when no memory has been allocated for it yet.

The "value" property exists, however, even if it is empty. To test if a
field is empty, you must compare it to an empty string:

if ( document.formName.fieldName.value == "" )
{
//empty
}

Laurent

Alternately, you can compare the length of the object's value to 0 .

Thomas 'PointedEars' Lahn · Oct 17, 2003

null is the value that an object has when it hasn't been initialized,

No, that is `undefined', the primitive sole value of the Undefined type.
Try

var a;
alert(typeof a);

`null' is a special object literal, the primitive sole value of the
Null type. It "represents the null, empty, or non-existent reference."
Try

alert(typeof null);

See
<http://devedge.netscape.com/library/manuals/2000/javascript/1.5/guide/ident.html#1008306>

<http://www.ecma-international.org/publications/standards/Ecma-262.htm>
ECMAScript Edition 3 (on which JavaScript 1.5 is based upon), sections
4.3.9 to 4.3.12

in other word when no memory has been allocated for it yet.

There is *always* memory allocated for a variable/object/property,
otherwise it would not be accessible (at least memory for an entry
in the global hash table must be allocated). AFAIK this is
independent of the programming language used.

PointedEars

Richard Hockey · Oct 18, 2003

chirs said:
I try to test a field to see if it's empty. But it prints "It is not
null". Why and how can I fix it?

<html>
<head>
</head>
<body>
<input type="text" name="box1">

<script>
if (box1.value != null) {document.write("It is not null")}
else {document.write("empty")}

give this a try

<script type="text/javascript">
// build regular expression object to find empty string or any number of
spaces
var blankRE=/^\s*$/;

function CheckEmpty(TextObject)
{
if(blankRE.test(TextObject.value))
{
alert('box1 is empty or contains only spaces.');
TextObject.focus();
}
}
</script>

and in the form

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How to test an empty input box?

chirs

Laurent Bugnion, GalaSoft

Jerry Park

Thomas 'PointedEars' Lahn

Richard Hockey

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