JavaScript Patterns 3.4 Array Literal

Array Literal Syntax

To avoid potential errors when creating dynamic arrays at runtime, it's much safer to stick with the array literal notation.

Array Constructor Curiousness

When you pass a single number to the Array() constructor, it doesn't become the value of the first array element.

// an array of one element

var a = [3];

console.log(a.length); // 1

console.log(a[0]); // 3

// an array of three elements

var a = new Array(3);

console.log(a.length); // 3

console.log(typeof a[0]); // "undefined"

// using array literal

var a = [3.14];

console.log(a[0]); // 3.14

var a = new Array(3.14); // RangeError: invalid array length

console.log(typeof a); // "undefined"    

Clever uses of the Array() constructor

 

var white = new Array(256).join(' '); 

Check for Array-ness

Array.isArray([]); // true

// trying to fool the check with an array-like object

Array.isArray({

    length: 1,

    "0": 1,

    slice: function () {}

}); // false

if (typeof Array.isArray === "undefined") {

    Array.isArray = function (arg) {

        return Object.prototype.toString.call(arg) === "[object Array]";

    };

}