Resolved How do i to filter dots in a texbox using javascript

[arunkumar93]

I want to alert the user if he enters only dots without any alphabets or numerals in a textbox using javascript.
If the input contains dots in between alphabets and numerals the javascript should not alert the user.I have a javascript which alerts the user even if dots are present in between alphabets and numerals.
Can any1 Help me..Below is my script:

function addressValidation(obj)
{
var regex = new RegExp("[.]");
if(obj.value.match(regex))
{
alert("Dot is not allowed");
obj.focus();
return false;
}
}

[Old Pedant]

What about if the user enters only dashes? Or only commas? Or only equal signs???

Would
====.=====
be legal?

Would
abc=def
be legal?

Can you be more specific about what *IS* legal??

[arunkumar93]

I need to prevent only dots.
Thanks for ur quick reply

[Philip M]

Like so:-

<script type = "text/javascript">

function addressValidation(obj) {
var regex = /^\./;
obj.value = obj.value.replace(/^\s+|\s+$/g,"");  // strip leading and trailing spaces
// OR IF YOU PREFER obj.value = obj.value.replace(/^[^a-z0-9\.]+/i,"");  // strip leading all non-alphanumeric characters (except dots)
if(obj.value.match(regex)) {
alert("Dot is not allowed");
obj.focus();
return false;
}
}

</script>

. in a regex means "any character". A literal dot is \.

Some people, when confronted with a problem, think "I know, I'll use regular expressions." Now they have two problems." — Jamie Zawinski.


You can test your regular expressions at: http://www.claughton.clara.net/regextester.html

[Old Pedant]

Philip's trick is a neat one: After getting rid of the leading/trailing spaces, he is simply checking to see if the dot is the first character left. If it is, then it's no good.

So his code *DOES* allow

a.b
3.x
=.=
$.$

and it PREVENTS

.
.b
.6
.=
.$

But it *also* allows

a.
2.
=.
$.

Is that what you want?

[arunkumar93]

The code shud PREVENT the below format also:

.
.b
.6
.=
.$

Thanks & Regards
Arun

[Philip M]

Originally Posted by Old Pedant

But it *also* allows

a.
2.
=.
$.

Is that what you want?

"If the input contains dots in between alphabets and numerals the javascript should not alert the user."

I have made a modification to the code but like you I am unclear if characters other than alpha-numeric are allowed. My alternative deletes them in the start position in the string.

[arunkumar93]

Thanks for ur Code.
Actually i have another onkeypress function to prevent all other special characters except dots.

[Old Pedant]

*POSSIBLY* this would do it???

function addressValidation(obj) {
    var regex = /(^\s*\.|\.\s*$)/;
    if( regex.test( obj.value ) {
        alert("Neither leading nor trailing dot is allowed");
        obj.focus();
        return false;
    }
    return true;
}

Combined the "strip spaces" so it's all done with one regex.

[Philip M]

Originally Posted by Old Pedant

*POSSIBLY* this would do it???

function addressValidation(obj) {
    var regex = /(^\s*\.|\.\s*$)/;
    if( regex.test( obj.value ) {
        alert("Neither leading nor trailing dot is allowed");
        obj.focus();
        return false;
    }
    return true;
}

Combined the "strip spaces" so it's all done with one regex.

You are getting tired or your brain is becoming weak.

That will not block .Old Pedant (dot followed by anything except a space). As I understand it the OP's requirement is simple - no leading dot(s). Dots between alphanumeric characters are OK.

In any case there is a typo:-

if( regex.test( obj.value ) ) {

I cannot understand this passion for crowding several different tests into one regex. It simply makes it harder to test and debug.

Just stick with the code I gave you in Post#4, with the following modification if trailing as well as leading dots are not allowed:-

var regex = /^\.|\.$/;

[arunkumar93]

Hi Philip,

Can you explain these two lines for me?

var regex = /^\./;
obj.value = obj.value.replace(/^\s+|\s+$/g,"");

Thanks & Regards
Arun

[Philip M]

Originally Posted by arunkumar93

Hi Philip,

Can you explain these two lines for me?

var regex = /^\./;
obj.value = obj.value.replace(/^\s+|\s+$/g,"");

Thanks & Regards
Arun

var regex = /^\./; // ^ means "at the start of the string". \. means "a dot character". So the regex means "match a dot character at the start of the string".

obj.value = obj.value.replace(/^\s+|\s+$/g,""); // means strip (delete or replace by nothing "") all space characters (\s+) at the start (^) or (|) the end ($) of the string. The g switch means "global", that is replace all matches rather than just the first one.

[Old Pedant]

Originally Posted by Philip M

That will not block .Old Pedant (dot followed by anything except a space).

?????
Adapted to just use a passed in string instead of form field:

<script>

function addressValidation(str) {
    var regex = /(^\s*\.|\.\s*$)/;
    if( regex.test( str ) ) {
        alert(str + "\nNeither leading nor trailing dot is allowed");
        return false;
    }
    alert(str + "\nOKAY");
    return true;
}

addressValidation(".Old Pedant");

addressValidation("                              .Old Pedant");

addressValidation("truly.     ");
</script>

But, yes, I did miss a right parenthesis.

[Philip M]

As you say, DOH! I misread it as var regex = /(^\s+\.|\.\s+)/; Sorry.

[arunkumar93]

Hi Philip,

<script type = "text/javascript">

function addressValidation(obj) {
var regex = /^\./;
obj.value = obj.value.replace(/^\s+|\s+$/g,"");  // strip leading and trailing spaces
// OR IF YOU PREFER obj.value = obj.value.replace(/^[^a-z0-9\.]+/i,"");  // strip leading all non-alphanumeric characters (except dots)
if(obj.value.match(regex)) {
alert("Dot is not allowed");
obj.focus();
return false;
}
}

</script>

In this is code can you change regex so it allows anything which starts with dot.

.b
.6
.=
.$


Thanks & regards
Arun