Reach nested array item using recursion - javascript

Question

I'm trying to reach the center of a nested array using recursion. This is part of a larger problem I'm trying to solve. I'm sure the solution is somewhat elementary. I've been learning JS/web dev and am stumped.

Here's my code:

var j = [[[["hey!"]]]];
function getNested(obj) {
for (var i = 0; i < obj.length; i++) {
 if (Array.isArray(obj[i])) {
 obj = obj[i];
 getNested(obj);
 } 
 return obj[i];
 } 
}

The function is supposed to return the 'hey!' string, but I can't seem to get it right.

• millimoose: Why is there a for loop if you'll only ever find the first innermost nested element and return it? How is your code recursive?
• Kevin Bowersox: What if there is more than one element in any of the nested arrays?
• Matt Ball: I don't see a place where getNested calls itself, be it directly or through mutual recursion.
• Cᴏʀʏ: What is findType? If you're looking for recursion, switch out that line for return getNested(obj)
• biera: I can't see recursion in your code. getNested() should call itself somewhere. What if your array looks like that ["hey1",[[["hey!", "hey2"]]]] for example? What should be returned?

Answer 1

You are close, just switch out the findType(obj) for return getNested(obj[i]). This will give you a recursive function that drills down into the array until the item in the array is not another array. Also, the for-loop was unnecessary, given your example input.

This will only work if your nested arrays have exactly one element. Others have expressed this in the comments.

var j = [[[["hey!"]]]];
function getNested(obj) {
 if (Array.isArray(obj)) {
 return getNested(obj[0]);
 } 
 return obj;
}
var str = getNested(j);
console.log(str); // "hey!"

jsFiddle Demo

Answer 2

There is no need for recursion, a simple while loop will already do the trick

var j = [[[["hey!"]]]];
function getNested(obj) {
 while (Array.isArray(obj)) { obj = obj[0]; } 
 return obj;
}
var str = getNested(j);
console.log(str); // "hey!"

The recursive implementation has the nice property that it is purely functional though if you rewrite it like so:

var j = [[[["hey!"]]]];
function getNested(obj) {
 return Array.isArray(obj)? getNested(obj[0]): obj;
}
var str = getNested(j);
console.log(str); // "hey!"

Still its performance would be worse though.

• Udo Klein: It uses a loop instead of recursion. Thus it should perform significantly better for deeply nested arrays.
• Ilya: May be you shoud write There is NO need for recursion
• Udo Klein: The recursive solution has the only advantage that it could be written in a more compressed way like so: function getNested(obj) { return Array.isArray(obj)? getNested(obj[0]): obj; } Still its performance would be worse.