Regular Expression for negative and positive decimal numbers

Question

I'm trying to create a regular expression using javascript for react application that allow negative and positive decimal numbers and not allow enter any character.

I've been looking for examples, reading documentation but I dont know how make it.

This are the things that have to do:

allow negative and positive decimal numbers, I found this:

var re = new RegExp("^[+-]?[0-9]{0,900}(?:\.[0-9]{0,900})?$");

but I can write a character and show me true and add other character and show me false. console.log(re.test(value));

if is decimal and starts with zero show zero (0.232) and dont allow this (.232)

dont allow write characters, I've seen this /^\\d*$/

Answer 1

Looking at the documentation about RegExp it states that when using the constructor function, the normal string escape rules (preceding special characters with \\ when included in a string) are necessary.

Your regex would then match a dot which would match any character making for example a valid because the preceding [0-9]{0,900} matches zero - 900 times.

Your regex would become:

var re = new RegExp("^[+-]?[0-9]{0,900}(?:\\.[0-9]{0,900})?$");

To match negative and positive decimal numbers that should not start with a dot, you could use:

^[+-]?[0-9]+(?:\\.[0-9]+)?$

Which will match the beginning of the string ^ , an optional [+-]? , one or more digits [0-9]+ followed by an optional part which will match a dot and one or more digits (?:\\.[0-9]+)? and then the end of the string $ .

var re = new RegExp("^-?[0-9]+(?:\\.[0-9]+)?$");

 var re = new RegExp("^[+-]?[0-9]+(?:\\\\.[0-9]+)?$"); var strings = [ "1", "1.2", "0.232", ".232", "-1.2", "+1.2" ]; strings.forEach((s) => { console.log(s + " ==> " + re.test(s)); }); 

Answer 2

I use this:

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

• only numbers
• positive and negative
• dont allow .232