Regular Expression not working as expected in javascript

Question

I have following regular expression: ^-?([0-9]{0,3}$|[0-9]{0,2}\.?[0-9]{0,1}$)

It should not allow 4 digit number such as 4444. The expression is working fine if I try here, but in javascript, the code is not working as expected. It is allowing 4 digit numbers. All other validations work fine.

Here is my code:

http://jsfiddle.net/PAscG/

reg0str = "^-?([0-9]{0,3}$|[0-9]{0,2}\.?[0-9]{0,1}$)";
var reg0 = new RegExp(reg0Str);
if (reg0.test(temp)) return true;

UPDATE TO EXPLAIN Functionality:

I want to allow only 3 digits. So either I can allow only 1 digit after decimal and 2 before decimal or I can allow max of 3 digits before decimal and nothing after decimal.

So my first part:
[0-9]{0,3}$ I assume this should allow a max of 3 digits and only numbers.

Next part: [0-9]{0,2}\.?[0-9]{0,1}$ should allow max of 2 digits before decimal and a max of 1 digit after decimal.

What exactly is that regex supposed to do? Apart from the mistake (see my answer) it matches also the empty string, a minus, a dot, decimals with leading or trailing dot... — Bergi
– Bergi, Commented Aug 1, 2012 at 18:26

HBP · Accepted Answer · 2012-08-02 09:46:30Z

1

Following OP's clarification

The regexp is

/^-?(\d{0,3}\.?|\d{0,2)\.\d)$/

  ^        start of string
  -?       optional minus sign (use [-+]? if you accept a plus sign)
  (        start of OR group
    \d{0,3}  0 1, 2 or 3 digits
    \.?      optional decimal point
  |        OR
    \d{0,2}  0 1, or 2 digits
    \.       decimal point
    \d       final decimal
  )        end of OR grouping
  $        end of string

edited Aug 2, 2012 at 9:46

answered Aug 1, 2012 at 18:12

HBP

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1 Comment

RMN Over a year ago

Hi, Just to clarify. I want to allow only 3 digits. So either I can allow only 1 digit after decimal and 2 before decimal or I can allow max of 3 digits before decimal and nothing after decimal.

Zach Lesperance · Accepted Answer · 2012-08-01 17:34:00Z

1

Try this:

 var reg0str = "^\-?[0-9]{0,2}[\.]?[0-9]?$";

I'm not sure why, but the period seems to be being treated as the wildcard character if not encapsulated within a class.

Here's the updated jsfiddle

answered Aug 1, 2012 at 17:34

Zach Lesperance

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4 Comments

Bergi Over a year ago

Why does your solution need any backslashes at all?

Zach Lesperance Over a year ago

@Bergi The period is treated as a wildcard character in RegEx, and while it is not necessary to escape it within a character class, the backslash won't hurt anything

Bergi Over a year ago

You don't have a regex, you only have a string literal. No need to escape anything than backslashes and quotes. See also my answer.

Zach Lesperance Over a year ago

@Bergi Hmmm, you're right. The backslashes would be fine in a regex literal but in this case they serve no purpose (unless they were escaped also). Thanks

Bergi · Accepted Answer · 2012-08-01 18:51:00Z

1

"…\.…" is a string literal - the backslash escapes the dot to a dot and the regex dot matches a digit. You would need to escape the backslash to pass a string with a backslash in the RegExp constructor:

new RegExp("^-?([0-9]{0,3}$|[0-9]{0,2}\\.?[0-9]{0,1}$)")

or you use a regex literal (simplified, but still matching the same):

/^-?\d{0,2}\.?\d?$/

edited Aug 1, 2012 at 18:51

answered Aug 1, 2012 at 18:18

Bergi

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1 Comment

Zach Lesperance Over a year ago

Yup, you're right about the \.. Couldn't the RegEx be simplified to this then? new RegExp("^-?[0-9]{0,2}\\.?[0-9]?$");

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