Check nested objects with an array of keys

Question

I've got an array (target) with keys to a series of nested objects. I need to make sure there is a object there before I set a value to it later on. This code is working but only so far as I can be bothered to repeat it.

How can I do this for n number of keys in the array without repeating this switch to infinity?

for t, index in target
    switch i
        when 1
            if object[target[0]] is undefined
                object[target[0]] = {}
        when 2
            if object[target[0]][target[1]] is undefined
                object[target[0]][target[1]] = {}
        when 3
            if object[target[0]][target[1]][target[2]] is undefined
                object[target[0]][target[1]][target[2]] = {}
        when 4
            if object[target[0]][target[1]][target[2]][target[3]] is undefined
                object[target[0]][target[1]][target[2]][target[3]] = {}
        when 5
            if object[target[0]][target[1]][target[2]][target[3]][target[4]] is undefined
                object[target[0]][target[1]][target[2]][target[3]][target[4]] = {}
        when 6
            if object[target[0]][target[1]][target[2]][target[3]][target[4]][target[5]] is undefined
                object[target[0]][target[1]][target[2]][target[3]][target[4]][target[5]] = {}

Look into tree iteration with recursion.

Justin Thomas
– Justin Thomas

2011-03-27 19:17:10 +00:00
Commented Mar 27, 2011 at 19:17 — Justin Thomas
– Justin Thomas, Commented Mar 27, 2011 at 19:17

Adrien · Accepted Answer · 2011-03-27 22:01:31Z

1

caveat untested code from the top of my head. But this should work...

current = object
for t in target
  current = (current[t] ?= {})

Or a more javascripty version:

target.reduce ((o,t)-> o[t]?={}), object

The first one is more legible, the second more elegant imho (and does not pollute the scope with current).

answered Mar 27, 2011 at 22:01

Adrien

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1 Comment

Trevor Burnham Over a year ago

Note that Array::reduce isn't available in all browsers. Here's an implementation you can use as a fallback: diveintojavascript.com/core-javascript-reference/…

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