QUESTION: Arguments Object behavior in a Currying Fn

JavaScript
1

Hi guys! When I was working on my JS Arguments Optional Problem, I encountered this weird behavior of arguments object. Please see the code below:

function add1() {
	//put arguments passed in an array
	let args = Array.from(arguments);

	let sum = x => y => x+y;

  return sum(args);
}

let add2 = x => y => x+y;

add1(2)(2);     //returns '22'
add2(2)(2);    //returns 4

I am aware that parseInt() would fix this, but I would like to know what causes the arguments in add1() turn into strings?

It’d be great if someone could provide an explanation to this behavior.

Thanks!

2

The first argument of your sum() is an array [2]. The second argument is 2.
Adding them results the expression ([2] + 2).
Even though it doesn’t make any sense to add them, Javascript will try to add them by coercing array to string, which results ([2].toString() + 2).
Hence, your final output is '22'

So, trying to resolve this by calling parseInt() is a bad idea.

3

@gunhoo93 Thanks! Your explanation made sense to me. I ended up using sum(args[0]) instead to avoid using parseInt().

4

Why do you even need args?

5

I got curious and tried to play with the inputs. I used args so I could also use the function to solve add1(1,2,3) as well.

6

But given your implementation, add1(1, 2, 3) is impossible.

7

My bad for not including it in the snippet as I just wanted to focus my question on this particular part of my code which you’ve had answered already.

So thanks again and happy coding! :slight_smile: