Arrays
Array is an
ordered collection of the elements which stores the data.
Syntax:
There are 2 syntaxes for creating an empty array:
let arr = [];
let arr = new Array();
Ex
Mostly the
first syntax is used to create an array, We can initialize values as follows:
let fruits = [“Pineapple”, ”Mango”,
”Watermelon”];
Array
elements are ordered and starts with index 0 (zero)
We can
access array elements by its numbers
let fruits = [“Pineapple”, ”Mango”,
”Watermelon”];
document.write(fruits[0]);
document.write(fruits[1]);
document.write(fruits[2]);
Replacing
array values
We can
replace values as follows:
fruits [1] = “Guava”;
Above statement will replace
“Mango” with “Guava”.
We can add
elements into array as follows:
fruits[3] = “Orange”;
Above statement will add one
more element to array.
We can
calculate length of array:
document.write(fruits.length);
Above statement will calculate
the number of elements in an array.
Methods
Array support two operations of Stack
Push: adds an element to the end
Pop: removes an elements from the end
The new elements are added and removed from the
end only
These above methods works at the end of the
array
Pop:
extracts the last element from array and
returns it.
Example:
let fruits
= ["Apple", "Orange", "Pear"];
document.write(
fruits.pop() ); // remove "Pear" and display it
document.write(
fruits ); // Displays Apple, Orange
Push:
appends the element at the end of the
array.
Example:
let fruits
= ["Apple", "Orange"];
fruits.push(“Mango");
//adds “Mango” at the end of the array
document.write(
fruits ); // Apple, Orange, Mango
Here are 2 more methods that works at the start
of the array:
shift: removes the element from the start of
the array
unshift: add the element at the beginning of
the array
shift
removes the element from the beginning
of the array,
Extracts the first element and moves the second
position element to the first position
let fruits
= ["Apple", "Orange", “mango"];
document.write(
fruits.shift() ); // remove Apple and displays it
document.write(
fruits ); // Displays Orange, Mango
unshift:
add the element at the beginning of
the array.
Shifts the first position element to second
position and add new elements at first position
let fruits
= ["Orange", “Mango"];
fruits.unshift('Apple');
// adds Apple at the first position
document.write(
fruits ); // Apple, Orange, Mango
push and unshift methods can add multiple items
at a time.
let fruits = ["Apple"];
fruits.push("Orange", “Guava");
fruits.unshift("Pineapple",
“Mango");
// ["Pineapple", “Mango", "Apple",
"Orange", “Guava"]
document.write( fruits );
Traversing
an Array
We can traverse (to visit array elements) array
by using loops
Very traditional way to traverse is use of for
loop
Using for Loop
Lets see
example :
let arr =
["Apple", "Orange", "Pear"];
for (let i
= 0; i < arr.length; i++)
{
document.write(
arr[i] );
}
Using for ... of
Another
form of loop for array is for … of
let fruits
= ["Apple", "Orange", "Plum"];
// iterates
over array elements
for (let x
of fruits)
{
document.write(
x );
}
Above loop
iterates through array and x is variable which accepts value from fruits[0] to end of an Array
Using for ... in
As array are objects we can also iterate it by
using for … in as follows:
let arr =
["Apple", "Orange", "Pear"];
for (let
key in arr)
{
document.write(
arr[key] ); // Apple, Orange, Pear
}
In above
example key extracts index number from arr and and utilized for printing the
array
new Array()
There is one more syntax to create an Array
let arr = new
Array("Apple", “Mango", "etc");
If new Array is called with a single
argument which is a number, then it creates an array without items, but
with the given length.
let arr = new
Array(2); // will it create an array of [2] ?
document.write(
arr[0] ); // undefined! no elements.
document.write(
arr.length ); // length 2
new Array(number) has all
elements undefined.
Multidimensional
Array
To create
multidimensional array there are 2 methods
Method 1 : Create 1 Dimensional array and then
add that array in another 2 Dimensional array
For Example:
•
let
arr1 = ["Ajay", 24, 18000];
•
let
arr2 = [“Mayur", 30, 30000];
•
let
arr3 = [“Mehak", 28, 41000];
•
let
arr4 = [“Rajni", 31, 28000];
•
let
arr5 = [“Yuvraj", 29, 35000];
Here we
have created 5 array elements
Here we create again 1 Dimensional array which consist array elements
let salary =
[arr1, arr2, arr3, arr4, arr5];
Above statement create multidimensional array of size 3*5 (3 columns and 5
rows)
Method 2:
we can directly assign multidimensional array
For
Example:
let salary
= [
["Ajay",
24, 18000],
[“Mayur",
30, 30000],
[“Mehak",
28, 41000],
[“Rajni",
31, 28000],
];
Here we
have created 2 D array with size 3*4 (3 columns and 4 rows).
We can also
initialize array by using commas on the separate line
Accessing
Multidimensional Array
Below code
is used for accessing multidimensional array
for (let i
= 0, l1 = salary.length; i < l1; i++)
{
// This
loop is for inner-arrays
for (let j
= 0, l2 = salary[i].length; j < l2; j++) {
// Accessing
each elements of inner-array
document.write(
salary[i][j] );
}
}
Here we are
printing the elements of 2D array variable i.e. salary
Strings
String is called as collection of characters. Usually string is called a character array.
In JavaScript the textual data is stored as a String. In JavaScript a single character is also treated as a String, there is no separate data type for storing a single character value.
There are 3 ways used to represent a String
1. Using Double Quotes
for example:
var str;
str="Welcome to Program";
2. Using Single Quotes
for example:
var str;
str='Welcome to Program';
3. Using Backticks Quotes
for example:
var str;
str=` Welcome to Program `;
Single quotes and Double quotes are used for the same purpose but the backticks are used for some special purpose.
Finding Character at by Index Position or Traversing a String
A String is a collection of characters or we may say it is a character array. As we say it is an array, we can traverse it or we may visit every character of a String.
To visit every character of a string we have to traverse through a String. To traverse a String there are two ways available
1. Traditional way to traverse string by an index position
for example:
string[index]
The above statement will print the character of the mentioned index position.
for example
var str = "Welcome to Program";
document.write( " Character at index position 3 is "+str[ 3 ] );
above statement will print 'c' , as 'c' is present at index number 3
2. Traverse string by an charAt() function
for example:
string.charAt(index);
The above statement will print the character of the mentioned index position.
for example
var str = "Welcome to Program";
document.write( " Character at index position 5 is "+charAt[ 5 ] );
above statement will print 'm' , as 'm' is present at index number 5.
String Function
String is collection of characters or is called as a character array, one can perform many operations on string. Operations like changing the case of string, replacing part of string, breaking string into parts, extracting some part from string, searching some part inside a string etc...
1. Changing the Case of a Sting
To change the case of a string following two functions are used
toUpperCase( ) is used to convert complete string into Uppercase Letters and toLowerCase( ) is used to convert complete string into Lowercase Letters.
for Example:
var str = "programming in javascript";
var str1 = "PROGRAM OF JAVASCRIPT";
var s = str.toUpperCase();
document.write( "Sting converted in UpperCase " +s );
//Above statement will print "PROGRAMMING IN JAVASCRIPT"
var s1 = str1.toLowerCase();
document.write( " String converted in LowerCase " +s1 );
//Above statement will print "program of javascript"
2. Searching a Specific word into a String:
indexOf() function is used to search a specific word inside a given string. There are two syntax of the indexOf() function are as follows:
int indexOf ( word )
where word is a substring or word to be searched into a given string and it will search the word from beginning of the String
int indexOf ( word, index )
where word is a substring or word to be searched into a given string and index is the location from where the search will begin
Above both functions will return a number,
if the substring or word is found, it will return the starting index number of the substring or word
if not found in the string then it will return the -1
for example:
var str = " Welcome to JavaScript Program " ;
document.write ( str.indexOf ( " Welcome " ) ) ;
//above statement will print 0 because Welcome is present at index number 0.
document.write ( str.indexOf ( " welcome " ) ) ;
//above statement will print -1, because welcome is not present in String as the search is case sensitive
document.write ( str.indexOf ( " Program " ) ) ;
//above statement will print 22 because Welcome is present at index number 22.
indexOf ( ) will search the first occurrence of the substring or word. remaining occurrences are remained unsearched.
3. Separating or dividing specific part of the string
Separating or dividing a string is also known as slicing a part of the string, 3 methods are available to divide a string into parts or to separate a part from a string.
slice, substring and substr
slice ( )
Syntax:
string slice ( begin_index , end_index );
it will return a part of string from begin index to end index (but it will not include end index character in the separated string)
for example:
var str = " JavaScript Program " ;
document.write ( str . slice ( 0, 5 ) );
above statement will print JavaS and it will not include 'c' as it is at index number 5 which is not included by slice.
If there is no end_index provided, it will slice the complete string from the begin_index up to the last index of the string.
var str = " JavaScript Program " ;
document.write ( str . slice ( 4 ) );
above statement will print Scipt Program, as the end_index is not mentioned in above example.
substring ( )
Syntax:
string substring ( begin_index , end_index )
it almost works similar like slice ( ) function, the added advantage is, we can put the begin_index value greater than end_index value.
for example:
var str = " JavaScript Program ";
document.write( str . substring ( 0, 5 ) );
document.write( str . substring ( 5, 0 ) );
above statements will print the same output JavaS
substr ( )
Syntax:
string substr ( begin_index , length )
this function returns a substring starting with the begin_index and specified length characters. This method allows us to specify the number of characters (length) instead of the end_index.
for example:
var str = " JavaScript Program " ;
document.write ( str . substr ( 3, 6 ) );
above statement will print the output aScrip, as it starts to divide separate a part of string from begin_index i.e. 3 and the mentioned length i.e. 6 number of characters.
4. Converting a number into a String:
To convert a specified or given number into a string toString ( ) function is used.
toString ( ) function converts number format to string format.
for example:
var value = 2000;
var str = value.toString ( );
above statement converts number 2000 to string 2000.
5. Convert string into a number:
To convert string into a number parseInt ( ) function is used.
for example:
var str = "2000";
var value = parseInt(str);
above statement converts "2000" into a number 2000. so that any mathematical operation can be performed with the value.
6. Replacing a part of string:
To replace a specified part of a string in given string replace ( ) function is used. This function do not make changes in the original string instead it returns a newly updated string. It replaces only the first occurrence of the specified string/word. To replace all the occurrences we need to take support of regular expressions.
Syntax:
string replace ( old_word, new_word )
Above statement replaces the old_word present in the string with the new_word specified and retuns newly updated string.
for example:
var str = " Welcome to JavaScript Program ";
var s = str . replace ( "Program" , " Language" );
document.write ( s );
above statement will print the output Welcome to JavaScript Language, it will replace Program word with Language word and returned a new String Welcome to JavaScript Language
replace ( ) function is a case sensitive function so it will not replaced the word with case sensitive details. To replace case sensitive word regular expression /i is used.
for example:
var str = " Welcome to JavaScript Program ";
var s = str . replace ( /program/i , " Language" );
document.write ( s );
above statement will print the output Welcome to JavaScript Language, it will replace program word with Language word and returned a new String Welcome to JavaScript Language
To replace all the occurrences of the old_word regular expression /g is used.
for example:
var str = "Sumit is a good athlete, Sumit runs very fast, Sumit covers 100 meter distance in 9 seconds ";
var s = str . replace ( /Sumit/g , "Raghav" );
document.write ( s );
above statement will replace all the occurrences of Sumit and replace it with Raghav and the output will be Raghav is a good athlete, Raghav runs very fast, Raghav covers 100 meter distance in 9 seconds
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