Only allow numbers and one decimal in textbox

Arc

Hey guys. I am trying to figure out a script that only allows users to input numbers and 1 decimal in a textbox using javascript without poping up an alert.

Basicaly, if they try to enter anything else or more than one decimal it just doesn't enter.

I am not sure where to start on this so any input is welcomed.

Thanks!

I thought about using the isNAN thing, but this would be much better.

Weedpacket

A regexp would do the job easily enough. [0-9].?[0-9] (will also allow "" and ".", note, but those can be checked for later: both are perfectly valid contents for the field while the number is being typed). Or every time a key is pressed, check that it's a digit or a ".". If a "." is typed and there is a "." already present in the field, and ignore the new one. Again, checking for a lone "." would have to wait until later.

JPnyc

isNAN wouldn't work here, since anything entered into a txtBox is string, and JS will see it as such and return NaN as true even if it is a number. Regex is the way to go here.

goldbug

Regex seems like overkill......wouldn't isNaN work just fine in conjunction with parseFloat??

if (isNaN(parseFloat(number))) { // do whatever scolding you see fit }

Arc

Thanks for the input guys.

So theres not a way to check the contents of the textbox and see if there's already a "." in there? Surely there is...My JS skills are crap, but couldn't you do a

if(inStr(ducument.form1.txtNumber,".") don't allow another...? Of course InStr is not a JS method that I know of, but it basicaly checks to see if a certain character is in the string.

Regex has always been real confusing to me, can you guys spell it out a little better for me?

Thanks a lot for the help.

I am sure this would come in handy to many programmers.

Arc

goldbug wrote:
Regex seems like overkill......wouldn't isNaN work just fine in conjunction with parseFloat??
if (isNaN(parseFloat(number))) { // do whatever scolding you see fit }
??

If I can avoid it I would rather not prompt after the input is finished, but just avoid it in the first place.

Thanks for the input though, I may have to go that route.

JPnyc

Might be possible, I have to ruminate on it. You might be able to test keycode onkeydown event. Pretty involved though, maybe too involved for your purposes

Weedpacket

Arc wrote:
So theres not a way to check the contents of the textbox and see if there's already a "." in there?

Sure there is; that's what I said you could do. What I said you couldn't do is reject a "." keystroke if the field is empty; a field that contains only a "." isn't a valid decimal, but the user might have just started typing ".5".

Arc

Ok so how would the function look exactly? I know how the logic should work, but I am not good enough at JS to figure out the exact syntax.

I assume I would use the OnKeyDown Event and call a Method like

function checkIsNum(formName,txtName){

var y = document.formName.txtName.value;
var filter = [0-9].?[0-9];
if (!filter.test(y)) document.formName.txtName.length -=1;

if there is already a "." then document.formName.txtName.length -=1;

}

That's about as close as I can get to psuedo code that shows what I mean.

Any input is much appreciated!

JPnyc

if there is already a "." then document.formName.txtName.length -=1; translates to
if(filter.indexOf('.')!=-1) document.formName.txtName.length --;

Arc

Thanks for the input. So far I have

function checkIsNum(){
var y = document.form1.txtSubject.value;
var filter = [0-9].?[0-9];
if (!filter.test(y)) document.form1.txtSubject.length -=1;
if(filter.indexOf('.')!=-1) document.form1.txtSubject.length --;
}

But apparently there is an issue with the filter var..... Is there a good tutorial for regex or can anyone show me the right thing to put there?

Thanks!