Nested objects, preventing "cannot get value of 'undefined'"

Question

Let's say I have an object called John with many other nested objects inside and I am trying to access them following way

if (john.address.highstreet) {
    var highstreet = john.address.highstreet
}

but if address property is null, then I will get an error

unable to get property 'highstreet' of undefined

and my function execution stops

Is there a way of accessing nested properties without making many nested if statements like it's shown below:

if (john.address) {
    if (john.address.highstreet) {
        var highstreet = john.address.highstreet
    }
}

I'd use something like lodash's [get](https://lodash.com/docs/4.17.4#get) — Paolo Moretti, Jan 10 '17 at 16:26

score 6 · Answer 1 · answered Jan 10 '17 at 16:23

6

The standard way would be

if (john.address && john.address.highstreet) {
    var highstreet = john.address.highstreet
}

If address is undefined then that is what will be returned.

answered Jan 10 '17 at 16:23

Euan Smith

2,102
1
16
26

thank you! That seems like the best way of doing it. – Grisha Gevorkyan Jan 10 '17 at 16:25
1

Note that this works because Javascript boolean operators are [short-circuiting](https://en.wikipedia.org/wiki/Short-circuit_evaluation). – Charles Wood Jan 10 '17 at 16:25
indeed. Hence why it is `&&` rather than just `&` - same convention as C – Euan Smith Jan 10 '17 at 16:26

score 1 · Answer 2 · edited May 23 '17 at 12:13

1

You probably want to use a bit more clever way of accessing these properties. Something like getPropertyByString("john.address.highstreet"). This function could return null or undefined if the path can't be resolved.

As in Alnitak's response

So your code could look just like this:

var highstreet = getPropertyByString("john.address.highstreet");

edited May 23 '17 at 12:13

Community

1
1

answered Jan 10 '17 at 16:26

strah

6,702
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score 0 · Answer 3 · answered Jan 10 '17 at 16:27

0

An alternative could be to use a try-catch-block.

try {
    var highstreet = john.address.highstreet;
} catch (err) {
    // do error handling
}

answered Jan 10 '17 at 16:27

Andre

385
1
13

score 0 · Answer 4 · answered Jan 10 '17 at 16:29

0

You can also use hasOwnProperty method to check for property

if(john.hasOwnProperty("address") && john.address.hasOwnProperty("highstreet"))
{
var highstreet = john.address.highstreet
}

answered Jan 10 '17 at 16:29

Satish Kumar sonker

1,250
8
15

Nested objects, preventing "cannot get value of 'undefined'"

4 Answers4