How to return null in Javascript function

TL;DR

Assuming we only need to apply a straight forward modification, I would avoid too much syntactical sugar and just write it this way:

function divide(num1, num2) {
  if (arguments.length < 2) {
    return null;
  }
  return num1/num2;
}

If we want to make it simple and elegant, I would write it this way (requires ES6 features):

const divide = (...args) => args.length < 2 ? null : args[0] / args[1];

Explanation

Improvement steps in vanilla JS (ES5 and before)

• Using function arguments: this is simply an array like object that will magically appear inside your function, which contains the arguments you have passed to the function.

function divide(num1, num2) {
  if (arguments.length < 2) {
    return null;
  }
  return num1/num2;
}

While this is a great solution for the problem there are a downsides to it, if you wanted to switch to arrow function arguments object doesn't appear.

• **Using ternary operator**you can farther more reduce the code by using the ternary ? which is best suitable for simple if statements

function divide(num1,num2) {
  return arguments.length < 2 ? null : num1 / num2;
}

Improvement steps in ES6

• Using spread (in this case it is actually called rest): the ... can be used to either collect items into an array known as rest, or expand an array known as spread.

function divide(...args) {
  return args.length < 2 ? null : args[0] / args[1];
}

JavaScript will collect all the arguments passed to the function and put them into an array called args, I like this better since the reader can see where is args defined.

• using arrow function: there are many difference between arrow and normal function, but many prefer it since it is shorter, and since we have a one-liner function why not use it.

const divide = (...args) => args.length < 2 ? null : args[0] / args[1];

On a final note all the previous solutions has a downside that we are only checking for length of arguments but not contents of arguments, lets assume that someone sent undefined into one of the first two arguments, you'll have 2 arguments but one of them is kinda missing and you'll get NaN since number of arguments is 2.

function divide(num1, num2) {
	  if (num1 === undefined || num2 === undefined) {
return null;
  }
  return num1/num2;
}

Demo

function divide1(num1, num2) {
	  if (arguments.length < 2) {
	    return null;
	  }
	  return num1/num2;
	}
	
function divide2(num1,num2) {
	  return arguments.length < 2 ? null : num1 / num2;
	}
	
	
function divide3(...args) {
	  return args.length < 2 ? null : args[0] / args[1];
	}


const divide4 = (...args) => args.length < 2 ? null : args[0] / args[1];


const test = (cb) => {
  console.log("-------->" + cb.name)
  console.log(cb());
  console.log(cb(1));
  console.log(cb(1, 2));
  console.log(cb(1, undefined));
  console.log(cb(1, null));
  console.log(cb(1, 2, 3));
};

test(divide1);
test(divide2);
test(divide3);
test(divide4);