Recursive Array Reversal Javascript

Question

So we are practicing functional javascript in my programming class with this assignment and I just can't get it to work right. Any advice in making this code work would be appreciated. Everything but the body was given for me to use. Here is what I have come up with: (It is always sending me just the first array index content rather than all of them reversed. I tried changing it to

 if(arr.length <= 1) return arr;

but that never hits the base case.)

function ReverseArray(arr) {
//base case
if(arr.length == 1)
{
 return arr[0];
}
if(arr.length == 0)
{
 return 0;
}
var head = arr.pop;
var newArr = [head, ReverseArray(arr)];
return newArr;
}

• epascarello: if(arr.length = 1) WRONG and if(arr.length = 0) wrong, You are assigning
• Andy: Deleted my answer because I realised you were meant to use recursion.
• jfriend00: Even if your function worked, your function returns an array so after one iteration, you'll have this [end0, [....]]. After two iterations, you'll have this [end0, [end1, [...]]] and it will keep nesting arrays further and further. Your approach will not work. You need a new design. Perhaps you want to use .concat() to add two arrays together rather than embedding one in another. If you want help with a new design, you will have to better describe the rules of the assignment since arr.reverse() already exists to do this.
• David Conrad: if (arr.length < 2) return arr;
• Dave: possible duplicate of Reverse array function with one parameter. (JavaScript)

Answer 1

x = y <--assignment
z == y <-- comparison 

Looking at your code:

if(arr.length = 1) 

needs to be

if(arr.length == 1)

same with the zero check

---

AND you are not calling pop

var head = arr.pop;

you need to parenthesis

var head = arr.pop();

Answer 2

This is the most precise and clean way to do it in a single line with the ternary operator.

function reverse(arr) {
 return arr.length < 2 ? arr : [arr.pop()].concat(reverse(arr));
}
console.log(reverse([4, 3, 3, 1]));

Answer 3

Here's a runnable example with a working function. FYI there is also a built-in function that will do this for you.

I think other than the confusion with assignment/comparison operators, when you were building the result array, you should be using Array.concat() to concatenate your array, instead you were building a new array where the second item was an array itself.

var a = [1,2,3,4,5];
console.log(ReverseArray(a));
function ReverseArray(arr) {
 if(arr.length < 2) {
 return arr;
 } else {
 return [arr.pop()].concat(ReverseArray(arr));
 }
}