What is the way of declaring an array in JavaScript?

The preferred way is to always use the literal syntax with square brackets; its behaviour is predictable for any number of items, unlike Array‘s. What’s more, Array is not a keyword, and although it is not a realistic situation, someone could easily overwrite it:

function Array() { return []; }

alert(Array(1, 2, 3)); // An empty alert box

However, the larger issue is that of consistency. Someone refactoring code could come across this function:

function fetchValue(n) {
    var arr = new Array(1, 2, 3);

    return arr[n];
}

As it turns out, only fetchValue(0) is ever needed, so the programmer drops the other elements and breaks the code, because it now returns undefined:

var arr = new Array(1);