Setting number of elements of arrays

Question

In the Javascript course, a lesson says you can use the syntax "var arr = new Array(3);" to declare an array and tell it how many elements with contain, then populate it. But Array constructor can take a list of elements to populate it on creation. Is there an exception when the constructor takes just one whole number? Because that syntax looks like a valid way to create an array with only one element: the number 3.

Answer 1

If you declare more than one parameter when creating array. Example.
var a = new Array( 1, 2 );
It's is seen as an Array constructor. Declaring a single parameter like in your example will been seen as an array with 3 empty index's. To avoid getting confused or forgetting. You can use this to kinda visually separate the syntax in a sense.
var arr = [];
arr.length = 3;