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 :

1. It should allow positive numbers.
2. It should allow max 13 numbers before decimal point
3. It should allow max two number after decimal.
4. It should allow . (dot) with number like a .5
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)); 

Answer 1

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)); 

Answer 2

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+)$/ )

Answer 3

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 ie

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

Answer 4

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));