i wrote that piece of code but it something wrong

Question

function typeCheck(varName) {
if (isNaN(varName)) {
alert("please enter a number");
}
}
//----------------------------------------------
function square() {
var side = prompt("please enter the side of your square");
typeCheck(side);
if (side === "") {
alert("Please fill all the boxes");
squereFormuala();
} else if (side === null) {
alert("Goodbye");
} else {
var result = side * side;
alert("the area of your square is " + result);
}
}

when I enter a string is now supposed to say "please enter a number" but what happens is it says "please enter a number", I hit enter and then it says to me "the area of your square is NaN."

please help

Answer 1

'var side' is always a string.
The 'prompt' function returns a string, so you need to parse it to int or float, before the calculation.

What happens:
When you enter some value (let say it is "abcdef") it goes to check, whether it's NaN and print 'please enter a number', because it is a string, then in the if condition:
1. side === "" is false - the string is not empty ("abcdef")
2. side === null is false - it is a string
3. else block (no matter what) do:
var result = side * side, or ("abcdef" * "abcdef") which returns 'NaN'.