Array construction is conventionally done via literal notation such as [] or [1, 2, 3]. Using the new Array() is discouraged as is new Array(1, 2, 3). There are two reasons for this. The first is that a single supplied argument defines the array length, while multiple arguments instead populate the array of no fixed size. This confusion is avoided when pre-populated arrays are only created using literal notation. The second argument to avoiding the Array constructor is that the Array global may be redefined.

The one exception to this rule is when creating a new array of fixed size, e.g. new Array(6). This is the conventional way to create arrays of fixed length.

Invalid:

// This is 4 elements, not a size 100 array of 3 elements
const a = new Array(100, 1, 2, 3);

const b = new Array(); // use [] instead

Valid:

const a = new Array(100);
const b = [];
const c = [1, 2, 3];