Javascript/React 中 function 末尾的 [] 是什么意思？

Question

Could someone give me the direction where to look, or let me know what does the square brackets mean at the end of the function. Is there a different way how this can be re-written?

Code Example:

  useEffect(() => {
if (user) {
  router.push('/profile');
}
 }, [user]);

So the part which I am trying to understand is the [user].

Can this be re-written differently? What does it mean from the code perspective?

Answer 1

This is called an Array literal .

An Array is an object that represents the concept of an indexable sequence of values . A literal is a syntactic element of the programming language that allows one to "literally" write down an object value, as opposed to programmatically constructing it.

Here's an example of the difference between programmatically constructing an array and directly writing down the same array:

const ary1 = Array.from({ length: 10 }, (_, i) => i);
const ary2 = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9];