Any value that starts with a digit is validated as number

The number validator validates any number that starts with a digit, e.g. 1a is accepted. This seems to be a problem of the value to number conversion:

let parsed = parseFloat(value);
if (this.isType(parsed)) return parsed;

return NaN;

From https://www.ecma-international.org/ecma-262/6.0/index.html#sec-parsefloat-string:

parseFloat may interpret only a leading portion of string as a Number value; it ignores any characters that cannot be interpreted as part of the notation of an decimal literal, and no indication is given that any such characters were ignored.

What about changing the code to this:

let parsed = parseFloat(value);
if (parsed == value) return parsed;

return NaN;

[shoutcool]

This bug should be threated with high severity. Such a basic check must not fail in a validation library.

[paintedbicycle]

Just to add another voice - I was very shocked to see a string (for example: ‘12’) pass the number check. I was also very confused as to why the string ‘12F’ would pass my check of:

var number = yup.number().required().positive().integer();

I honestly thought I had an error in my code and spent a while trying different things.

• I did not expect a string to be allowed to be a number at all
• and I was extremely confused on why a number that also has a letter in it would pass!