regex - How do I include negative decimal numbers in this regular expression?

Question

How do I match negative numbers as well by this regular expression? This regex works fine with positive values, but I want it to also allow negative values e.g. -10, -125.5 etc.

^[0-9]d*(.d+)?$

Thanks

Answer 1

You should add an optional hyphen at the beginning by adding -? (? is a quantifier meaning one or zero occurrences):

^-?[0-9]d*(.d+)?$

I verified it in Rubular with these values:

10.00
-10.00

and both matched as expected.

let r = new RegExp(/^-?[0-9]d*(.d+)?$/);

//true
console.log(r.test('10'));
console.log(r.test('10.0'));
console.log(r.test('-10'));
console.log(r.test('-10.0'));
//false
console.log(r.test('--10'));
console.log(r.test('10-'));
console.log(r.test('1-0'));
console.log(r.test('10.-'));
console.log(r.test('10..0'));
console.log(r.test('10.0.1'));