In ES2015 is there a way to directly access object properties without checking for undefined?

Question

In ES5 whenever I want to get some property I need to first check that it exists like this:

if (typeof floob.flib !== 'undefined') {
    // do something
}

even worse is that for nested properties you have to manually check for the existence of every property down the dotted path.

Is there a better way to do this in ES2015?

"In ES5 whenever I want to get some property I need to first check that it exists" --- no you don't need that. Btw, to check if the property is there - there is an `in` operator. Your check is prone to false negatives. — zerkms, Jun 17 '16 at 01:25
@zerkms can you please expand on how the "in" operator can be used to tell me if a nested attribute exists on an object? — Duke Dougal, Jun 17 '16 at 01:30
@zerkms without wanting to criticise, but I think the idea of StackOverflow is to give answers that are a full explanation rather than terse bullet points. — Duke Dougal, Jun 17 '16 at 01:34
That is the very reason I haven't posted an answer but a comment. — zerkms, Jun 17 '16 at 01:34
Possible duplicate: http://stackoverflow.com/questions/32139078/null-safe-property-access-in-es6-es2015 — Alex KeySmith, Jul 13 '16 at 08:18

score 2 · Answer 1 · answered Jun 17 '16 at 01:39

If it is just a single depth property name - you don't need typeof, you may just compare the value with undefined.
Your solution is prone to false negatives: it may think there is no a property with a given name, while there is one. Example: var o = { foo: undefined };
If you need to check if the path exists in the nested objects - you still need to implement recursion/loop/or use any library that does either for you.
ES2015 did not bring anything new to solve this problem easier.

score 2 · Answer 2 · answered Jun 17 '16 at 01:55

2

If you have lodash available, you can use _.get(obj, path, defaultValue) (https://lodash.com/docs#get)

answered Jun 17 '16 at 01:55

darthtrevino

choz · Answer 3 · 2016-06-17T02:29:53.560

-1

By using typeof,

typeof floob.flib === 'undefined'

equals to,

floob.flib === undefined

I assume you want to check whether floob.flib has a value, and if it does, you want to perform an operation with it.

However, in JS, there's almost simpler way to achieve this.

E.g.

if (floob.flib) {
   // 'floob.flib' is NOT 'null', 'empty string', '0', false or 'undefined'
}

This also works well if you want to assign variable with ternary ( ?: ) operators.

var str = floob.flib ? 'exists' : 'does not exist';

Or even using logical OR ( || )

var str = floob.flib || '<= either null, empty, false, 0 or undefined';

Note that unless floob.flib does not produce ReferenceError exception, the code above should work just fine.

edited Jun 17 '16 at 02:29

answered Jun 17 '16 at 01:48

choz

`'floob.flib' is NOT 'null', 'empty string', or 'undefined'` should include `false`. – Jun 17 '16 at 02:27
@torazaburo Lol.. Yes that should include too.. with `0` also.. Thanks for pointing that out.. – choz Jun 17 '16 at 02:29

3 Answers3