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Features of an Array

• An array declaration allocates sequential memory blocks.
• Arrays are static. This means that an array once initialized cannot be resized.
• Each memory block represents an array element.
• Array elements are identified by a unique integer called as the subscript / index of the element.
• Like variables, arrays too, should be declared before they are used. Use the var keyword to declare an array.
• Array initialization refers to populating the array elements.
• Array element values can be updated or modified but cannot be deleted.

Declaring and Initializing Arrays

Syntax

var array_name[:type[]]        //declaration 
array_name = [val1,val2,..,valn]   //initialization
var array_name[:type[]] = [val1,val2,…,valn]//declared and initialized

Note: default datatype in declaration is any

Example:

var array1:string[]
array1 = ["t","u","t","o","r","i","a","l","s","p","o","t","s"]
var array2:string[] = ["t","u","t","o","r","i","a","l","s","p","o","t","s"]

After compiling:

"use strict";
var array1;
array1 = ["t", "u", "t", "o", "r", "i", "a", "l", "s", "p", "o", "t", "s"];
var array2 = ["t", "u", "t", "o", "r", "i", "a", "l", "s", "p", "o", "t", "s"];
 

Accessing Array Elements:

Syntax :

array_name[the_index] = value

Example:

console.log(array1[0])
console.log(array1[1])

Result:

[LOG]: t 
[LOG]: u 

Array Object

Syntax:
Syntax 1:

var arr_name[:type[]] = new Array()  

Example:

var arr_name:number[] = new Array()  
console.log(arr_name)

Result:

[LOG]: [] 

Syntax 2:

var arr_name[:type[]] = new Array(array_size)  

Example:

var arr_name:number[] = new Array(4)  
console.log(arr_name)

Result:

[LOG]: [ null, null, null, null ] 

Syntax 3:

var arr_name[:type[]] = new Array(value1,value2,...,valueN)  

Example:

var arr_name:number[] = new Array(1,2,3,4)  
console.log(arr_name)

Result:

[LOG]: [ 1, 2, 3, 4 ] 

Array properties:

length – dimension of array

Array Methods

S.No.	Method & Description
1.	concat() Returns a new array comprised of this array joined with other array(s) and/or value(s).
2.	every() Returns true if every element in this array satisfies the provided testing function.
3.	filter() Creates a new array with all of the elements of this array for which the provided filtering function returns true.
4.	forEach() Calls a function for each element in the array.
5.	indexOf() Returns the first (least) index of an element within the array equal to the specified value, or -1 if none is found.
6.	join() Joins all elements of an array into a string.
7.	lastIndexOf() Returns the last (greatest) index of an element within the array equal to the specified value, or -1 if none is found.
8.	map() Creates a new array with the results of calling a provided function on every element in this array.
9.	pop() Removes the last element from an array and returns that element.
10.	push() Adds one or more elements to the end of an array and returns the new length of the array.
11.	reduce() Apply a function simultaneously against two values of the array (from left-to-right) as to reduce it to a single value.
12.	reduceRight() Apply a function simultaneously against two values of the array (from right-to-left) as to reduce it to a single value.
13.	reverse() Reverses the order of the elements of an array — the first becomes the last, and the last becomes the first.
14.	shift() Removes the first element from an array and returns that element.
15.	slice() Extracts a section of an array and returns a new array.
16.	some() Returns true if at least one element in this array satisfies the provided testing function.
17.	sort() Sorts the elements of an array.
18.	splice() Adds and/or removes elements from an array.
19.	toString() Returns a string representing the array and its elements.
20.	unshift() Adds one or more elements to the front of an array and returns the new length of the array.

Array Destructuring

Syntax

var [value1,value2,...,valueN] = arr_name 

Example:

var arr_name:number[] = new Array(1,2,3,4)  
var [value1,value2] = arr_name 
console.log(value1,value2)

After compiling:

"use strict";
var arr_name = new Array(1, 2, 3, 4);
var value1 = arr_name[0], value2 = arr_name[1];
console.log(value1, value2);

Result:

[LOG]: 1,  2 

Multi-dimensional arrays

TypeScript supports multidimensional arrays. The simplest form of the multidimensional array is the two-dimensional array (2D-array).

Example:

var arr_name:number[][] = new Array([0,1,2],[3,4,5],[6,7,8])  
console.log(arr_name[0][0])
console.log(arr_name[0][1])
console.log(arr_name[0][2])
console.log(arr_name[1][0])
console.log(arr_name[1][1])
console.log(arr_name[1][2])
console.log(arr_name[2][0])
console.log(arr_name[2][1])
console.log(arr_name[2][2])

Result:

[LOG]: 0 
[LOG]: 1 
[LOG]: 2 
[LOG]: 3 
[LOG]: 4 
[LOG]: 5 
[LOG]: 6 
[LOG]: 7 
[LOG]: 8 

Passing arrays to functions
You can pass to the function a pointer to an array by specifying the array’s name without an index.

Example:

var names:number[] = new Array(0,1,2,3)  
function myFunc(arr_names:number[]) {
   for(var i = 0;i<arr_names.length;i++) { 
      console.log(arr_names[i]) 
      arr_names[i]++
   }  
}  
myFunc(names)
console.log(names) 

Result:

[LOG]: 0 
[LOG]: 1 
[LOG]: 2 
[LOG]: 3 
[LOG]: [ 1, 2, 3, 4 ] 

Return array from functions
Allows a function to return an array

Example:

function myFunc():number[] {   
   return new Array(0,1,2,3)  
}  
var names = myFunc()
console.log(names) 

Result:

[LOG]: [ 0, 1, 2, 3 ]