TypeError: Cannot read properties of null (reading ‘length’)

Being the Javascript newbie that I am…
Javascript errors are still a mystery, more so if using Chrome/Chromium.
With Firefox the error was actually more clear.

TypeError: Cannot read properties of null (reading 'length')
means you have a variable that you’re checking it’s property ‘length’ to be a certain value but the variable is null.


In this case localStorage’s ‘urls’ key or rather value of the ‘urls’ key was empty and JSON.parse transformed that to null.
So if you check for urls.length to be greater than 0, you can’t do it and receive this error message.

How do you solve it?

This is the Javascript (and Typescript) way to check if a variable isn’t null and then check its property if it isn’t.
I know, logically this makes no sense, because it’s a logical AND. But hey, it’s Javascript so you don’t have to understand, you have to believe. 😉 HTH

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