CodeSignal - Is Digit

isDigit.js

/*
Determine if the given character is a digit or not.

Example

For symbol = '0', the output should be
isDigit(symbol) = true;
For symbol = '-', the output should be
isDigit(symbol) = false.
*/

function isDigit(symbol) {
    if(symbol >= 0) {
        return true;
    }
    else {
        return false;
    }
}