Javascript validation with Null

[krismath]

I am unable to have the "null" value working for the validation of the
text field.
The code is able to validate if the sid value is having one,two,three
spaces....but not more..it is sloppy coding...but it works....any
pointers to improve the code.

sid = document.form1.StudentID.value;
if (sid.length == 0 || sid == " " || sid ==" " || sid ==" " || sid
==" ")
{
alert("Student ID is Missing " + sid);
return false;

But when I am using, the sid is accepting values. with spaces.

if (sid.length == 0 || sid == null)
{
alert("Student ID is Missing " + sid);
return false;
}

[Richard Cornford]

kr******@gmail.com wrote:

I am unable to have the "null" value working for the validation
of the text field.
Not true, the - null - value is working exactly as programmed.
The code is able to validate if the sid value is having one,two,three
spaces....but not more..it is sloppy coding...but it works....any
pointers to improve the code.

sid = document.form1.StudentID.value;
if (sid.length == 0 || sid == " " || sid ==" " || sid ==" " || sid
==" ")
{
alert("Student ID is Missing " + sid);
return false;
Why is it acceptable for the user to enter 5 or more spaces?

This type of validation would usually be done with a regular
expression.
But when I am using, the sid is accepting values. with spaces.

if (sid.length == 0 || sid == null)

<snip>

The - null - value does not equal any string value, even a sting made
up of white space, or an empty string.

Richard.

[Laurent Bugnion]

Hi,

kr******@gmail.com wrote:

But when I am using, the sid is accepting values. with spaces.

if (sid.length == 0 || sid == null)

This will cause an error if sid is null. If sid is null, then trying to
access its length property will crash the script, thus the validation
will fail.

JavaScript (and other C-like languages) has a nice feature: If you use a
logical OR, and if the first term of the expression is true, then the
second term won't be evaluated. This is an optiization for speed
(because no unnecessary evaluation is made), but also allows such
constructs:

if ( sid == null || sid.length == 0 )

In that case, if sid is null, then sid.length is not evaluated so there
is no error. If sid is not null, then sid.length doesn't cause an error.

HTH,
Laurent
--
Laurent Bugnion, GalaSoft
Software engineering: http://www.galasoft-LB.ch
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