Comment by Jason Knight on "How to create nested child objects in Javascript from array?" | Hashnode

Jason Knight

The less code you use, the less there is to break

Nov 10, 2017

Whilst it's fun to see all the complex answers, mine's a bit more draconian... you probably won't find a faster routine for doing this. It exploits that objects are always passed by reference in JavaScript, even during assignment.

function nest(arr) {
    for (var obj = {}, ptr = obj, i = 0, j = arr.length; i < j; i++)
        ptr = (ptr[arr[i]] = {});
    return obj;
}

No recursive calls, no fancy mapping/each, no nested function calls/multiple functions, no long-winded objectAssign, no foreach or other methods that won't work in legacy browsers. Just a simple FOR loop and assignment. Should work all the way back to IE5.

Jason Knight

The less code you use, the less there is to break

Nov 10, 2017

Oh, and just to be precise, this is the LITERAL answer to your question. I would NEVER do this in production code.

function messed(arr) {
    if (arr.length > 0) {
        var ptr = window[arr[0]] = {};
        for (var i = 1, j = arr.length; i < j; i++) ptr = ptr[arr[i]] = {};
    }
}

Setting a property on window behaves like setting a global variable -- so that basically creates a = { b : { c : {} } } in global scope if you feed it ['a', 'b', 'c']. That first array index will be the new variable name.

This — ptr = (ptr[arr[i]] = {}); Wow! Lots of claps! 👏

And you're right, it is faster (at least by a factor of 10, from a basic benchmark) compared to the functional approach, using reduce!

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