Question

I found this regexp for validating floats. But I cant see how 2-1 will accepted. The below evaluates to true. I can’t use parseFloat because I need to be able to accept “,” instead of “.” also. I wrote re2, same result though.

var re1 = new RegExp("^[-+]?[0-9]*\.?[0-9]+$");
console.log(re1.test("2-1"));

var re2 = new RegExp("^([0-9]+)\.([0-9]+)$");
console.log(re2.test("2-1"));

Answer 1

If you generate the regex using the constructor function, you have to to escape the backslash, i.e. \ becomes \\:

var re1 = new RegExp("^[-+]?[0-9]*\\.?[0-9]+$");

Another option is to use the literal syntax which doesn’t require escaping:

var re1 = /^[-+]?[0-9]*\.?[0-9]+$/