oddEvenRecursive.js

function isEven(number) {
    if (number === 0) return true;
    else if (number === 1) return false;
    else {
        if (number < 0) return isEven(number + 2);
        else if (number > 35663) return "number too big";
        else return isEven(number - 2);
    }
};

isEven(35663)

• Unless your not suppose to for the sake of this exercise. Use the modulus operator https://en.wikipedia.org/wiki/Modulo_operation It would make this function one line long.
• In general try to limit the number of places that your code can exit. Try to keep it down to one. There are exceptions to this rule as well. When having another return can help lower cyclomatic complexity for instance.
• Label your constants. Having a random number like 35663 in a program without any explanation would immediately make me raise an eyebrow.
• In general avoid recursion if you can. You could do this just as easily with a for loop, and recursion is slower. (Don't take my word for it, try it!) It is good to think recursively in some cases. In fact some of the best algorithms are recursive, but if you don't need it, try avoiding it first.
• Missing ";"
• (almost) always put the stuff inside a bracket on the next line. -- readability.
• Math.abs() http://stackoverflow.com/questions/9353929/get-the-absolute-value-of-a-number-in-javascript always use libraries when possible.

This was the prompt:

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We’ve seen that % (the remainder operator) can be used to test whether a number is even or odd by using % 2 to check whether it’s divisible by two. Here’s another way to define whether a positive whole number is even or odd:

Zero is even.

One is odd.

For any other number N, its evenness is the same as N - 2.

Define a recursive function isEven corresponding to this description. The function should accept a number parameter and return a Boolean.

Test it on 50 and 75. See how it behaves on -1. Why? Can you think of a way to fix this?

// Your code here.

console.log(isEven(50));

---

• I included that number because it's the maximum number allowed that I was able to use before I had a stack overflow (though I was wondering if this might vary in different operating environments?). I played with it for a while finding how large a number it could support (since I've never written a recursive function before). But anyways, it was just me screwing around and handling a case to prevent out of control recursion causing an error.
• I generally put stuff in a bracket on the next line, but when refactoring, I (aesthetically) feel like if it fits neatly on one line, that makes it more readable (the parent conditions stand out more, making the flow more obvious). Is it not ok in certain circumstances, specifically for very simple code?
• How would you write this to avoid having various return statements?