how to manage [object HTMLDivElement] and get its content?

Question

I have saved an array in local storage and trying to use it but when I console.log the localstorage.getitem it returns
[object HTMLDivElement] I have tried to use .innerhtml or [...] on it but they didn't work. Btw, since it's an array, I have to use JSON.stringify(movieWatchlistArray):

 localStorage.setItem("key",JSON.stringify(movieWatchlistArray))
 let str =localStorage.getItem("key")
 console.log(JSON.parse(str) )

But when I do this, it will return an empty object inside an array while when I console.log the original array it's fine so I tried to do it without JSON part, it worked but returns a string of
[object HTMLDivElement]

 localStorage.setItem("key",movieWatchlistArray)  
 let str =localStorage.getItem("key")
 console.log(str)

So how to get the content of [object HTMLDivElement] I have used .innerhtml but it says can't use .innerHTML on undefined .