reactjs - Javascript check if an string is a valid number

Question

What is the correct way to check if a string is valid number in javascript?

Normally we use isNaN(str), this works great in all cases but excepts,

Current behaviour:

isNaN("1") = false, is a number,
isNaN("1 ") = false, But this is a string.

What is the correct approach to deal with this?

Expected results:

isNotNumber("1") = false
isNotNumber("1 ") = true

question from:https://stackoverflow.com/questions/65843474/javascript-check-if-an-string-is-a-valid-number

Answer 1

That's a bit of an odd case. I don't know of any native JS solution for this, but you could do the following:

function isNotNumber(subj: string): boolean {
  const nr = +subj;
  
  return isNaN(nr) || nr.toString().length !== subj.length;
}

example with tests