Testing Existence of a Sparse Array Element in JavaScript?

Question

What's the best way to test for the existence of an array element in a structure several layers deep? For instance:

if (typeof arr[a][b][c] === 'undefined') { ...do something... }

If [a] or [b] don't exist, we won't be able to test for [c].

Are there underscore or lodash functions to handle this?

Answer 1

It you need it in many places you can create a function:

function get(obj, props) {
  return props.reduce(function(x, p) { return x && x[p] ? x[p] : null }, obj)
}

if (get(arr, [a, b, c])) ...

Works with objects and arrays:

var obj = [0, {a: [0, 'value', 2]}, 2]
get(obj, [1, 'a', 1]) //=> 'value'
get(obj, [1, 'a', 8]) //=> null