Javascript regex positive negative decimal number

Question

I need a regex that would match a positive and negative decimal value, empty string ('') and also minus only ('-'). Since I need it inside the function that handles the change of a numeric field and in order to add a negative value the user firstly adds the "-" or deletes the old value (""), I need to match all these 3 conditions.

So, to sum up, the regex should allow:

• positive & negative decimal values (also 0)
• "" (empty string)
• "-" (minus string)

What I have until now is:

function sanitizeInputValue(value: string) {
  var re = new RegExp('^$|^-?\\d{1,9}(\\.\\d{1,2})?$');
  return value.match(re) === null ? 0 : value;
}

Answer 1

Use javascript's built in Number to convert the string into a numeric value right before you return from the function.

Also, I modified your regex so that it can accept input like .23 and 0.2345 .

 function sanitizeInputValue(value) { var re = new RegExp('^$|^-?(\\d+)?(\\.?\\d*)?$'); return value.match(re) === null? 0: Number(value); } console.log(sanitizeInputValue("-23")); // -23 console.log(sanitizeInputValue("42.123")); // 42.123 console.log(sanitizeInputValue("-.34")); // -0.34 console.log(sanitizeInputValue("")); // 0 console.log(sanitizeInputValue("-8.")); // -8 console.log(sanitizeInputValue("-8.4")); // -8.4

Answer 2

You can make matching the digits with decimal parts optional so you would also match the hyphen only ^$|^-?(?:\d{1,9}(\.\d{1,2})?)?$

As then all parts are optional, you can omit the ^$ and then all parts are optional.

^-?(?:\d{1,9}(?:\.\d{1,2})?)?$

Explanation

• ^ Start of string
• -? Optional hyphen
• (?: Non capture group
  • \d{1,9} match 1-9 times a digit
  • (?:\.\d{1,2})? Optionally match a dot and 1-2 digits
• )? Close non capture group and make it optional as well
• $ End of string.

Regex demo

 var re = new RegExp("^-?(?:\\d{1,9}(?:\\.\\d{1,2})?)?$"); [ "", "-", "1", "1.2", "test", "1234567890", "1.123", "-2", "-2.6" ].forEach(s => console.log(s + " --> " + re.test(s)));

Edit

As you also want to match -8. and don't want to limit the amount of digits, you could use:

^-?(?:\d+\.?\d*)?$

Explanation

• ^ Start of string
• -? Optional -
• (?: Non capture group
  • \d+\.?\d* Match 1+ digits, optional dot and 0+ digits
• )? Close group and make it optional
• $ End of string

Regex demo

 var re = new RegExp("^-?(?:\\d+\\.?\\d*)?$"); [ "-8.", "", "-", "1", "1.2", "test", "1234567890", "1.123", "-2", "-2.6" ].forEach(s => console.log(s + " --> " + re.test(s)) );

Answer 3

function sanitizeInputValue(value) {
  var re = /^$|\-?[0-9]\d*(\.\d*)?|-/;
  return value.match(re) ? value : 0;
}