Checking for undefined in if statements, leading to uncaught errors because item in if is undefined. What to do?

Question

I see there are not many oboe tags used on SO, but please help if you can, this is more of a general javascript question about handing uncaught errors for undefined. Thanks!~

I am using Oboe.js to stream data to webpage from a MongoDB atlas collection. In the MongoDB JSON, some of the _ids have a path of item.image.filename which is a path to an image. Some do not have item.image.filename, as not all of the streamed items need an image. The loading stops when there is an undefined value and I see an error in the console.

I would expect that if there is not a value present that oboe would just carry on to the next record as its default behavior. However, the _ids without the image path are throwing an exception in the if statement I am using to rule them out. I want to be clear that item.image.filename is not there with no value in it or set to null, it just doesn't exist. From what little I know of MongoDB, the flexibility to have each item be unique is one of its big advantages.

I believe I have hit on all manners of checking for this with if statements, even using a try catch block, but when compiled, the if statement itself is throwing this error: oboe-browser.min.js:5 Uncaught Error: Cannot read property 'filename' of undefined at oboe-browser.min.js:5 . The if else block would render html without the image if undefined, otherwise render it.

One way to fix this would be to add a item.image.filename to each record, but I would rather not, there are a lot of records, that's my last resort. Seems there is a better wait to sort this out.

Here is what I have tried:

if(!item.image.filename)

if(item.image.filename === undefined)

if(item.image.filename == 'undefined')

if(item.image.filename == undefined)

if(item.image.filename === 'undefined')

if(item.image.filename === null)

if(item.image.filename == null)

I took an alternative route like if(item.image.filename !== undefined) both with and without quotes, and with null too.

Thanks for the help!

Answer 1

You'll want to use typeof:

if(typeof item !== 'object' || typeof item.image !== 'object' || item.image.filename === undefined){
  console.log("undefined as far as you're concerned");
}

What you need to know is you cannot do a === undefined test on a variable that has not been declared. But it is okay to do that test on an Object property that doesn't exist, as long as the Object does exist.

Answer 2

try something like this:

if(item.image.filename in this)

or

if(!(item.image.filename in this))

where this is an object or array