Regular expression for negative float

Hi Guys,
   Need a regular expression for  floating point numbers, should allow negative numbers as well.
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write some examples of formats you would like to accept.
Do you need only true or false with an alert in false case?
Here a simple check:


function isFloat(theValue){
  return (/^-?\d+(\.\d+)?$/).test(theValue+'');


James RodgersWeb Applications DeveloperCommented:
try this to see if it fits your needs

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">

      function testFloat(){
                  alert("not valid");
            return false;

<form name="testForm" onSubmit="return testFloat()">
<input type="text" name="myFloat" value="">

<input type="submit" name="go" value="go">


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rasarajaAuthor Commented:
  what is the ^ for ? What is it negating ?
rasarajaAuthor Commented:
Oops ! Sorry is for begining .. that's fine..
rasarajaAuthor Commented:
Ooops ! Sorry it ..for the begining ...
rasarajaAuthor Commented:
Jester/NetGroove, there's a problem ... having (\.\d+)? is accepting anything after a dot !

It is taking

Anything !!

Maybe we can do something like this - /^ - \d+(\.)?(\d)+/
James RodgersWeb Applications DeveloperCommented:
change it to


That is already there:


function isFloat(theValue){
  return (/^-?\d+(\.\d+)?$/).test(theValue+'');

alert('1: '+isFloat(1));
alert('-100: '+isFloat(-100));
alert('12.5: '+isFloat(12.5));
alert('9.bbbbb: '+isFloat('9.bbbbb'));

The ^ is for string beginning.
The ? is a quatifier requestin maximum of one or none.
Imprtant is the $ at the end to request the end of the string. Otherwise you could realy add anything after the match.

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James RodgersWeb Applications DeveloperCommented:
thanks for the points
Regular grading is an A.
B is only in the school when you are the teacher.
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