javascript, test if nested attribute exists

Question

var foo = a.foo or {}
var bar = foo.bar or {}

It is tedious to do this for every level of nesting.

Can I somehow do instead?

var bar = a.foo.bar or {}

No, not really, since otherwise you would get property bar doesn't exist on undefined, you could however make a function that checks this — Icepickle, Oct 14 '16 at 09:16
You could do it with a small utility function as well (though I also believe Nina's code to be the easiest), like such: https://jsfiddle.net/Icepickle/85cbq9h1/ — Icepickle, Oct 14 '16 at 09:26

Nina Scholz · Answer 1 · 2016-10-14T09:19:59.840

2

You need a nested approach, you may have a look to logical operators and objects.

var bar = a && a.foo && a.foo.bar || {};

edited Oct 14 '16 at 09:19

answered Oct 14 '16 at 09:16

Nina Scholz

1

Won't this return false if `a` or `a.foo` is undefined. – evolutionxbox Oct 14 '16 at 09:18
Oh, javascript && operator does return full object, not the truth value. Thanks. – eugene Oct 14 '16 at 09:20

Bhojendra Rauniyar · Answer 2 · 2016-10-14T09:17:48.413

0

In javascript you need to use || to indicate for or.

var bar = a.foo.bar || {}; // However, a, a.foo may also be undefined

So, you need to check them using && operator to know if they all are defined:

var bar = a && a.foo && a.foo.bar || {};

edited Oct 14 '16 at 09:17

answered Oct 14 '16 at 09:16

2 Answers2