Regular expression for validating numbers

Only Digits:

unsigned (positive) whole number.

1): Any size or pattern using a set
function testExp(str) {
 var exp=/^ *[0-9]+ *$/;
    if (exp.test(str)) {
                alert('valid');
            }
   }

2): 3 to 5 digits.

function testExp(str) {
 var exp=/^\d{3,5}$/;
    if (exp.test(str)) {
                alert('valid');
            }
   }


The first regular expression allows one or more characters in the set [0-9] preceded or followed by any number of spaces within the length of the string. A number with leading and trailing spaces can be considered valid because conversion to numeric data will ignore the spaces.

if you dont want to allow spaces then use this
/^[0-9]*$/;

The second regular expression with the addition of {3,5} that restricts the data to only 3 to 5 digits.

signed integer:
 
1): Any size or pattern using a set
function testExp(str) {
 var exp=/^[-+]?[0-9]+$/;
    if (exp.test(str)) {
                alert('valid');
            }
   }

2): An optional sign and 3 to 5 digits
function testExp(str) {
 var exp=/^[-+]?\d{3,5}$/;
    if (exp.test(str)) {
                alert('valid');
            }
   }

Decimal or Float:
 
1): Any size or pattern using a set

function testExp(str) {
 var exp=/^[-+]?[0-9]+(\.[0-9]+)?$/;
    if (exp.test(str)) {
                alert('valid');
            }
   }

2): Limited number of whole digits and decimals

function testExp(str) {
 var exp=/^[-+]?\d{3,5}(\.\d{1,3})?$/;
    if (exp.test(str)) {
                alert('valid');
            }
   }