Negative match regex for positive and negative numbers with decimals

Question

I have regex expression which ensures that any characters which do not match the following criteria are replaced by an empty string:

• Must be a number.
• Optionally can be positive or negative.
• Optionally can have decimal values, but not a trailing decimal point.

My problem : I am unable to figure out how to preserve the negative sign if it is found in front of the number. My regex currently replaces all instances of the '-' by an empty string. I am missing something here to ensure this issue does not occur .

 var testId = document.getElementById('test'); var validate = value => { let regex = /([^\\d.-]+)|([^\\.?\\d]+)/g; return value.toString().trim().replace(regex, ''); }; // Note: in comments, the expected output var values = [ '12345', // 12345 '-12345', // -12345 '12345.6789', // 12345.6789 '-12345.6789', // -12345.6789 '-123-45.-6789', // -12345.6789 '$12345a6', // 123456 '-1abcde+^~2345.6*#zZ789', // -12345.6789 '50-00', // 5000 '$12345' // 12345 ]; values.forEach(value => { testId.innerHTML += `<p>${value} ==> ${validate(value)}</p>`; });

 <div id="test"></div>

Answer 1

You can use

return value.toString().trim().replace(/[^\d.-]+/g, '').replace(/^(-)|-/g, '$1');

Here,

• .replace(/[^\\d.-]+/g, '') - removes all chars other than digits, dots and hyphens
• .replace(/^(-)|-/g, '$1') - only keeps the first hyphen in the string and removes all other hyphens. The point is that (-) captures the hyphen at the start ( ^ means the start of the string) into Group 1 that you can access with $1 backreference from the replacement pattern, and |- means "OR a hyphen that will be only matched in a non-initial position.

See the JavaScript demo:

 var testId = document.getElementById('test'); var validate = value => { return value.toString().trim().replace(/[^\\d.-]+/g, '').replace(/^(-)|-/g, '$1'); }; // Note: in comments, the expected output var values = [ '12345', // 12345 '-12345', // -12345 '12345.6789', // 12345.6789 '-12345.6789', // -12345.6789 '-123-45.-6789', // -12345.6789 '$12345a6', // 123456 '-1abcde+^~2345.6*#zZ789', // -12345.6789 '50-00', // 5000 '$12345' // 12345 ]; values.forEach(value => { testId.innerHTML += `<p>${value} ==> ${validate(value)}</p>`; });

 <div id="test"></div>