JavaScript: Is string a number?

Just use the function isNaN(), which is standing for "is Not a Number". The function accepts a string and returns true if the string is not a number and false if the string is a number.

Here is a small example:

alert(isNaN("123")); //false
alert(isNaN("abc")); //true
alert(isNaN("1.0")); //false
alert(isNaN("1,0")); //true

"123" is a number, so "is Not a Number" is false. "abc" is not a number, therefore, the result is true.

With "1.0" and "1,0", you have to know, that in JavaScript, numbers are separated with a point instead of a comma. So, "1,0" is no number and in contrast, "1.0" is a number.
Last update on 2020-09-03 | Created on 2012-07-02