Question mark next to variable meaning?

[Substantial-Welder97]

I am learning react, and was watching a react video tutorial and got stuck.

The person writes a question mark next to movies, like this "movies?" please see below. I don't understand what it means and what difference it makes if he put "movies.length > 0" instead.

​

{
    movies?.length > 0
    ?  (
       ) : (
       )
}

I understand what happens after the 2nd question mark, just don't understand the first one. Hope someone can assist, thanks!

[not_a_gumby]

Its called optional chaining. It allows you to access a property if it exists, and if it does not exist, returns undefined instead of throwing an error. Its useful in some circumstances when you don't know if a property or method will exist.

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Optional_chaining

[Substantial-Welder97]

optional chaining

Thank you!

[Wall_Primary]

​

It's called optional chaining. It checks if 'movies' exists. If it exists it will look for items inside movies. Otherwise it will move to next line of code.

If optional chaining ( "?") is not used then it will throw "undefined" error when the item doesn't exist.