How to assert on something that is undefined?

Question

this is blowing up

if (myObject.myKey.myThing){

}

cannot read myThing of undefined

how can this be written in a way that if it is defined it goes into the if block, and if it not it does not?

Hopefully in future we will be able to use optional chaining https://github.com/tc39/proposal-optional-chaining — justMe, Aug 07 '18 at 12:00

score 0 · Answer 1 · answered Aug 07 '18 at 11:55

0

Add another check to see if myObject.myKey exists -

if (myObject.myKey && myObject.myKey.myThing){

}

answered Aug 07 '18 at 11:55

Rishikesh Dhokare

3,559
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yeh thought so, seems long though. but cheers – donut Aug 07 '18 at 11:55
@donut you can shorten that check to `((myObject.myKey || {}).myThing)` – chazsolo Aug 07 '18 at 11:57

score 0 · Answer 2 · answered Aug 07 '18 at 11:55

you would use the hasOwnProperty method, like so

if (myObject.hasOwnProperty('myKey')) {
   ...
}

You would want to use this as opposed to just checking the value of the keys because then if the value of that key is a false equivalent value your code won't run

How to assert on something that is undefined?

2 Answers2