What is the meaning of square brackets on a function parameter

Issue

Can someone explain me what is the meaning of [] in a function parameter, I don't get what the purpose of the [] on [fileEntry].

const onDrop = ([fileEntry]: any[]) => {
     fileEntry && fileEntry.file(file => processFile(file))
}

Does it convert the fileEntry to an array? I f yes why that won't work?

const onDrop = (fileEntry) => {
     fileEntry = [fileEntry]
     fileEntry && fileEntry.file(file => processFile(file))
}

Solution

It's destructuring - the function takes an array as its argument and fileEntry is the first entry of that array.

Simpler example (JavaScript):

const firstEl = ([el]) => el;

console.log(firstEl([a, b, c]));

Does it convert the fileEntry to an array? I f yes why that won't work?

No, it does the opposite. So the first line of your function is backwards. This is the equivalent of the first bit of code:

const onDrop = (fileEntry) => {
     [fileEntry] = fileEntry
     fileEntry && fileEntry.file(file => processFile(file))
}

Answered By - JLRishe