3. Arrays
Array inherits from Object.
Indexes are converted to strings and used as names for
retrieving values.
Not very efficient in most other cases.
The JavaScript Array object is a global object that is used
in the construction of arrays; which are high-level, list-like
objects.
One advantage: No need to provide a length or type
when creating an array.
4. Normally, arrays allocate a contiguous block of memory of
fixed length. However, in Javascript, arrays are:
Object types with special constructors and accessor
methods.
Which means, a statement like:
var arr = new Array(100000);
does not allocate any memory! In fact, it simply sets the value
of the length property in the array.
When you construct an array, you don't need to declare a
size as they grow automatically.
5. So, you should use this instead:
var arr = [];
Arrays in Javascript are sparse which means not all
the elements in the array may contain data. In
other words, only the elements that actually contain
data exist in the array. This reduces the amount of
memory used by the array. The values are located
by a key and not by an offset. They're simply a
method of convenience and not intended to be
used for complex numerical analysis.
Arrays in Javascript are not typed so the value of an
element can be an object, string, number, boolean,
function or an array.
6. Declaring and Allocating Arrays
JavaScript arrays are Array objects.
Creating new objects using the new
operator is known as creating an instance
or instantiating an object
Operator new is known as the dynamic
memory allocation operator
7. Declare + Initialize Arrays
Only declaration
var arr=[];
Using the conventional Syntax
var arr = [“a” , ”b” , ”c”];
Using the JavaScript Keyword new
var arr = new Array(“1”,”2”,”3”,”4”);
document.write(arr[0]+arr[1]+arr[2]+arr[3]);
9. Associative Array
//Associative array example
var person ={ firstName: "Frayosh", Lastname:"Wadia“ };
document.write(""+person["firstName"]+
“ ”+person["Lastname"] );
Javascript associative array is a type of array which
stores data using name value pairs
The array data can be accessed by specifying the key rather
than the index
Output : Frayosh Wadia
13. CONCAT
Javascript array concat() method returns a new
array comprised of this array joined with two or
more arrays.
Syntax:
The syntax of concat() method is as follows −
array.concat(value1, value2, ..., valueN);
Return Value:
Returns the length of the array.
14. //Array method Concat
<script>
var a=new Array("Hello");
var b=new Array("World");
document.write("<br>"+a.concat(b));
</script>
Output :Hello,World
15. Join
Javascript array join() method joins all the elements
of an array into a string.
Syntax
Its syntax is as follows −
array.join(separator);
Parameter Details
separator − Specifies a string to separate each
element of the array.
Return Value
Returns a string after joining all the array elements.
17. PUSH
Javascript array push() method appends the given
element(s) in the last of the array and returns the
length of the new array.
Syntax
Its syntax is as follows −
array.push(element1, ..., elementN);
Parameter Details
element1, ..., elementN: The elements to add to the
end of the array.
Return Value
Returns the length of the new array.
19. POP
Javascript array pop() method removes
the last element from an array and returns
that element.
Syntax
Its syntax is as follows −
array.pop();
Return Value
Returns the removed element from the array.
20. // Array method pop
<script>
var e=new Array(1,2,3,4);
e.pop();
document.write("<br>"+e);
</script>
Output :1,2,3
21. UNSHIFT
Javascript array unshift() method adds one or
more elements to the beginning of an array and
returns the new length of the array.
Syntax
Its syntax is as follows −
array.unshift( element1, ..., elementN );
Parameter Details
element1, ..., elementN − The elements to add to
the front of the array.
Return Value
Returns the length of the new array.
23. SHIFT
Javascript array shift()method removes the first
element from an array and returns that
element.
Syntax
Its syntax is as follows −
array.shift();
Return Value
Returns the removed single value of the array.
25. SORT
Javascript array sort() method sorts the elements of
an array.
Syntax
Its syntax is as follows −
array.sort();
Return Value
Returns a sorted array.
27. REVERSE
Javascript array reverse() method reverses the
element of an array. The first array element
becomes the last and the last becomes the first.
Syntax
Its syntax is as follows −
array.reverse();
Return Value
Returns the reversed single value of the array.
29. SLICE
Javascript array slice() method extracts a section of an
array and returns a new array.
Syntax
Its syntax is as follows −
array.slice( begin ,end);
Parameter Details
begin − Zero-based index at which to begin extraction
end − Zero-based index at which to end extraction.
Return Value
Returns the extracted array based on the passed parameters.
32. Javascript array splice() method changes the content of an array,
adding new elements while removing old elements.
Syntax
Its syntax is as follows −
array.splice(index, howMany, [element1][, ..., elementN]);
Parameter Details
index − Index at which to start changing the array.
howMany − An integer indicating the number of old array elements
to remove.
element1, ..., elementN − The elements to add to the array.
Return Value
Returns the extracted array based on the passed parameters.
Splice
33. Remove Values
//Splice method used for removing elements
var j=new Array("A","B","C","D","E");
j.splice(2,2);
document.write("<br>"+j);
Output :A,B,E
35. ADD & REMOVE
//Splice method used for adding and removing
elements
var j=new Array("A","B","C","D","E");
j.splice(2,2,"S","H");
document.write(“<br>"+j);
Output : A,B,S,H,E
36. IndexOf
Javascript array indexOf() method returns the first index at
which a given element can be found in the array, or -1 if it is
not present.
Syntax
Its syntax is as follows −
array.indexOf(searchElement, fromIndex);
Parameter Details
searchElement − Element to locate in the array.
fromIndex − The index at which to begin the search.
Defaults to 0, i.e. the whole array will be searched.
Return Value
Returns the index of the found element.
38. Javascript array lastIndexOf() method returns the last index at
which a given element can be found in the array, or -1 if it is not
present. The array is searched backwards, starting at fromIndex.
Syntax
Its syntax is as follows −
array.lastIndexOf(searchElement, fromIndex);
Parameter Details
searchElement − Element to locate in the array.
fromIndex − The index at which to start searching backwards.
Defaults to the array's length, i.e., the whole array will be
searched.
Return Value
Returns the index of the found element from the last.
LastIndexOf
39. // Array method :Last Index Of
<script>
var index = [8, 5, 8, 130, 44,8,16,15];
document.write("<br>"+ index.lastIndexOf(8,6));
</script>
Output :5
40. LENGTH
Javascript array length property returns an unsigned,
32-bit integer that specifies the number of elements
in an array.
Syntax
Its syntax is as follows −
array.length
Return Value
Returns the length of the array
41. // Array length returning the length of the
array
<script>
var ar=new Array("A","B","C","D","E","F","G");
document.write("<br>"+ar.length);
</script>
Output :7
42. Adding Elements
Javascript allows you to declare and empty array and add values later on
Eg. var cities=[];
cities[0]="Delhi";
cities[1]="Mumbai";
cities[2]="Chennai";
cities[3]="Bangalore";
or
You can simply add values during declaration
Eg. var cities=[“Delhi",“Mumbai",“Chennai",“Bangalore"];
or
Create an Array instance(new) and add values
Eg. var cities=new Array(“Delhi”,”Mumbai”,”Chennai”,”Bangalore”);
43. Deleting Elements
delete array[number]
Removes the element, but leaves a hole in the numbering.
Returns Boolean value
array.splice(number, 1)
Removes the element and renumbers all the following
elements. Returns the deleted value.
44. Deleting Elements
//deleting Elements using delete
var cities=["Delhi","Mumbai","Chennai","Bangalore"];
delete cities[1];
document.write("<br>Array after using delete :"+ cities);
document.write("<br>Displaying element at 1st position:"+cities[1]);
Output
Array after using delete :Delhi,,Chennai,Bangalore
Displaying element at 1st position:undefined
45. //deleting using splice
<script>
var cities=["Delhi","Mumbai","Chennai","Bangalore"];
document.write("<br>Deleted Element:"+cities.splice(1,1));
document.write("<br>Array after using splice:"+ cities);
document.write("<br>Displaying element at 1st position:"+
cities[1]);
</script>
Output
Deleted Element:Mumbai
Array after using splice:Delhi,Chennai,Bangalore
Displaying element at 1st position:Chennai