TypeScript Language Specification v1.5

interface Array {
length: number;
[x: number]: T;
// Other members
}
Array literals (section 4.6) may be used to create values of array types. For example
var a: string[] = ["hello", "world"];
A type is said to be an array-like type if it is assignable (section 3.10.4) to the type any[].
3.3.3 Tuple Types
Tuple types represent JavaScript arrays with individually tracked element types. Tuple types are written
using tuple type literals (section 3.7.5). A tuple type combines a set of numerically named properties with
the members of an array type. Specifically, a tuple type
[ T0, T1, ..., Tn ]
combines the set of properties
{
}
0: T0;
1: T1;
...
n: Tn;
with the members of an array type whose element type is the union type (section 3.4) of the tuple
element types.
Array literals (section 4.6) may be used to create values of tuple types. For example:
var t: [number, string] = [3, "three"];
var n = t[0]; // Type of n is number
var s = t[1]; // Type of s is string
var i: number;
var x = t[i]; // Type of x is number | string
Named tuple types can be created by declaring interfaces that derive from Array and introduce
numerically named properties. For example:
interface KeyValuePair extends Array { 0: K; 1: V; }
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