Array in ECMAScript 262

A sparse array.

Arrays in ECMAScript are sparse—they are not contiguous blocks of memory. This means that var foo = new Array(100000000); is valid, and will not crash your computer allocating gobs of memory.

Arrays auto-grow. Attempting to access an index greater than the length of the array simply returns undefined, not an error. Setting a value for an index greater than the length property causes the length to be one greater than the index set.

var foo = new Array(10);
if (foo.length==10){ //true }
foo[20]=3;
if (foo.length==21){ //true }

Arrays may be initialized either using the var foo = new Array(arraySize); constructor, or using the array literal notation, var foo = []; The latter is less bytes, and also faster. Additionally, it is possible to specify initial values of the array using the array literal notation:

var cars = [ 'Mustang' , 'Accord LX' , 'EarthDestroyer 2000' ];
if (cars.length==3){ //true }

The length property is read-write; changing its value to a new, lower value is a quick way to truncate an array, e.g. cars.length=0 empties out the array.