Javascript Regular expression for basic digits with decimal points?

Question

I am trying to use a regular expression to validate decimal values . I wrote below regular expression but it does not allowing first decimal with value like a .5 or .6 or .1

Regular Exp : /^\d[0-9]{0,13}(\.\d{1,2})?$/

Rules :

It should allow positive numbers.
It should allow max 13 numbers before decimal point
It should allow max two number after decimal.
It should allow .(dot) with number like a .5
It should not allow the .0

Example - Valid inputs

0
0.5
1.55
.5
1234567890123(13 numbers before decimal)
1234567890123.5
1234567890123.00

Example - invalid inputs

.(dot),
.0
1.234
5.
12345678901234(14 numbers before decimal)
12345678901234.56

const valid = [
  "0",
  "0.5",
  "1.55",
  ".5",
  "1234567890123",
  "1234567890123.5",
  "1234567890123.00",
];

const invalid = [
  ".",
  ".0",
  "1.234",
  "5.",
  "12345678901234",
  "12345678901234.56",
];

const rgx = /^\d[0-9]{0,13}(\.\d{1,2})?$/

console.log("Checking valid strings (should all be true):");
valid.forEach(str => console.log(rgx.test(str), str));

console.log("\nChecking invalid strings (should all be false):");
invalid.forEach(str => console.log(rgx.test(str), str));

Remove [0-9] from ~ \d[0-9]{0,13} ~ in your regex, then it will allow .5 or .6 or .1 etc — Thm Lee
– Thm Lee, Commented Mar 24, 2018 at 1:07
Your question is actually too broad since many other edge cases are missing. — Casimir et Hippolyte
– Casimir et Hippolyte, Commented Mar 24, 2018 at 1:42

CRice · Accepted Answer · 2018-03-24 00:54:31Z

4

I believe the following regex should meet all of your criteria:

^(\d{1,13}($|\.\d?\d$)|\.[1-9]\d?$)

first case: 1-13 digits followed either by nothing or by a "." followed by one or two digits

second case: a "." followed by a non zero digit and at most one other digit

const valid = [
  "0",
  "0.5",
  "1.55",
  ".5",
  "1234567890123",
  "1234567890123.5",
  "1234567890123.00",
];

const invalid = [
  ".",
  ".0",
  "1.234",
  "5.",
  "12345678901234",
  "12345678901234.56",
];

const rgx = /^(\d{1,13}($|\.\d?\d$)|\.[1-9]\d?$)/

console.log("Checking valid strings (should all be true):");
valid.forEach(str => console.log(rgx.test(str), str));

console.log("\nChecking invalid strings (should all be false):");
invalid.forEach(str => console.log(rgx.test(str), str));

edited Mar 24, 2018 at 0:54

CRice

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answered Mar 24, 2018 at 0:50

Oliver Too Eh

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Comments

Abslen Char · Accepted Answer · 2018-03-24 00:39:15Z

1

i think this should do most of your requirment but not all of them, limit to 9 decimal places

( /^(\d+\.?\d{0,9}|\.\d{1,9})$/ )

and this one with no decimal limit

( /^(\d+\.?\d*|\.\d+)$/ )

edited Mar 24, 2018 at 0:39

answered Mar 24, 2018 at 0:22

Abslen Char

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4 Comments

Eric Over a year ago

yes, I can't think of a better solution than handling the xxx.xx case and .xx case separately

Abslen Char Over a year ago

yes me too , i hope my input will help you slove the issue

Eric Over a year ago

I found out this case doesn't correctly match 5. input

Eric Over a year ago

I think it should be /^(\d+\.?\d{1,9}|\.\d{1,9})$/

Nick · Accepted Answer · 2018-03-24 05:01:34Z

1

The other answers don't allow for the case of .0x, which I presume is valid? I think you need to test for xxx[.xx] and .xx separately i.e.

^(\d{1,13}(\.\d{1,2})?|\.(0[1-9]|[1-9]\d?))$

answered Mar 24, 2018 at 5:01

Nick

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Comments

The fourth bird · Accepted Answer · 2018-03-24 11:05:43Z

To match your values you could use a non capturing group with an alternation using | and specify what you want to match.

^(?:\.[1-9][0-9]?|\d{1,13}(?:\.\d{1,2})?|.\d{2})$

This will also match .01 and not .0

Explanation

^ Begin of the string
(?: Non capturing group
- \.[1-9][0-9]? Match dot not followed by a 0 and then 0-9
- | Or
- \d{1,13} Match 1 - 13 digits
- (?: Non capturing group
  - \.\d{1,2} Match a dot and 1 or 2 digits
- )? Close non capturing group and make it optional
- | Or
- .\d{2} Match dot followed by 2 digits
) Close non capturing group
$ End of the string

const valid = [
  "0",
  ".01",
  "0.5",
  "1.55",
  ".5",
  "1234567890123",
  "1234567890123.5",
  "1234567890123.00",
];

const invalid = [
  ".",
  ".0",
  "1.234",
  "5.",
  "12345678901234",
  "12345678901234.56",
];

const rgx = /^(?:\.[1-9][0-9]?|\d{1,13}(?:\.\d{1,2})?|.\d{2})$/;

console.log("Checking valid strings (should all be true):");
valid.forEach(str => console.log(rgx.test(str), str));

console.log("\nChecking invalid strings (should all be false):");
invalid.forEach(str => console.log(rgx.test(str), str));

To not match .01 you could use:

^(?:\d{1,13}(?:\.\d{1,2})?|\.[1-9][0-9]?)$

const valid = [
  "0",
  "0.5",
  "1.55",
  ".5",
  "1234567890123",
  "1234567890123.5",
  "1234567890123.00",
];

const invalid = [
  ".",
  ".0",
  ".01",
  "1.234",
  "5.",
  "12345678901234",
  "12345678901234.56",
];

const rgx = /^(?:\d{1,13}(?:\.\d{1,2})?|\.[1-9][0-9]?)$/;

console.log("Checking valid strings (should all be true):");
valid.forEach(str => console.log(rgx.test(str), str));

console.log("\nChecking invalid strings (should all be false):");
invalid.forEach(str => console.log(rgx.test(str), str));

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