JavaScript II

JavaScript

Operator	Operation	Expression	Result
+	Add	2 + a	4
-	Substract	2 - a	0
*	Multiply	3 * a	6
/	Divide	3 / a	1.5
%	Modulus - division remainder	7 % a	1
++	Increment - increase by 1	a++	3
--	Decrement - decrease by 1	a--	1

Comparison Operators

Operator	Operation	Expression	Result
==	Equal to	a == b	false
!=	Not equal to	a != b	true
<=	Less than equal to	a <= b	true
>=	Greater than or equal to	a >= b	false
<	Less than	a < b	true
>	Greater than	a > b	False

Assignment Operators

a = 1, b = 2, and c = 3.

Operator	Operation	Result
=	a = b + c;	a = 5
+=	a += b;    // equivalent to a = a + b	a = 3
-=	a -= b;    // equivalent to a = a – b	a = -1
/=	a /= b;    // equivalent to a = a / b	a = 0.5
%=	c %= b;   // equivalent to c = c % b	c = 1
*=	a *= b;    // equivalent to a = a * b	a = 2

Logical or Boolean Operators

In the table below the variables have the following values: a = 1 and b = 2.

Operator	Operation	Expression	Result
&&	Logical and. Returns true only if both its first and second operands are evaluated to true.	a < 3 && b > 5	returns false as b > 5 is false
||	Logical or. Returns true if one of the two operands are evaluated to true, returns false if both are evaluated to true.	a < 3 || b > 5	returns true as a < 3 is true
!	Logical not. Unary operator that simply inverts the Boolean value of its operand.	!(b>5)	returns true

Bitwise operators in JavaScript

The table below summarizes the bitwise operators in JavaScript:

Operator	Usage	Result
Bitwise AND	a & b	Returns 1 for each bit position where both operands are 1
Bitwise OR	a | b	Returns 1 for each bit position where either operand is 1
Bitwise XOR	a ^ b	Returns 1 for each bit position where either but not both are 1
Left shift	a << b	Shifts in binary fashion all bits one position to the left; discarding the left bit and filling the right bit with 0.
Right shift	a >> b	Shifts in binary fashion all bits one position to the right, discarding the right bit. This operations maintains the original sign (+ or -).
0-fill right shift	a >>> b	Shifts in binary fashion all bits one position to the right, discarding the right bit and filling the left bit with 0.

JavaScript does not support an integer type,All numbers in JavaScript are stored in 64-bit floating point format i.e. double precision floating point. 

for loop

var count =0;
for (vari = 0;i < 10;i++) {
    count +=i;
}
alert("count = "+ count);         // => count = 45

while loop

var i =0;
count = 100;
while (i < count){
   i++;
}
alert("i = " +i);                 // => i = 100

switch statement

// switch statement
var day =new Date().getDay();
switch(day){
   case0:
      alert("Today is Sunday.");
      break;
   case1:
      alert("Today is Monday.");
      break;
   case2:
      alert("Today is Tuesday.");
      break;
   case3:
      alert("Today is Wednesday.");
      break;
   case4:
      alert("Today is Thursday.");
      break;
   case5:
      alert("Today is Friday.");
      break;
   case6:
      alert("Today is Saturday.");
      break;
   default:
      alert("Today is a strange day.");
}

if-then-else
var value =9;
if (value < 0){
   alert("Negative value.");
} elseif (value < 10){
   alert("Between 0 and 9, inclusive.");
} else{
   alert("Greater than or equal to 10.");
}

break and continue

for (vari = 0;i < 100;i++) {
   if(i <5) {
      continue;
   }else if(i >7) {
      break;
   }
   alert(i);         // => 5, 6, 7
}
try, catch

try {
    doesNotExist();
}
catch (ex){
    alert("Error: " + ex.message);    // => Error details
}

// JavaScript
function calculate (){
   varcount = 0;                     // function level scope
   ...                  
}

// JavaScript
var accept =true;       // global scope
if (accept === true){
   varcount = 0;       
}

// global scope   

varsay = function(){
    alert("Hello");
};
say();                          // => Hello

Next is an example of a function that is passed as an argument to another function:
var say =function() {
    alert("Hello");
};
function execute(callback){
    callback();
}
execute(say);                  // => Hello

And here is an example of a function that is returned by another function:
function go(){
    returnfunction() {
        alert("I was returned");
    };
}
var result =go();
result();                    // => I was returned

JavaScript is object-oriented, but class-less:

vartext = "excellent";
alert(text.substring(0,5));     // => excel

var count =20.1045;
alert(count.toFixed(2));        // => 20.10

Objects:

// Note: the use of new Object() is generally discouraged
var o =new Object();

o.firstName ="Joan";
o.lastName ="Holland";
o.age =31;

alert(o.firstName + " "+ o.lastName);  // => Joan Holland
alert(typeof o.age);                    // => number

delete o.firstName;
alert(o.firstName + " "+ o.lastName);  // => undefined Holland

for (varprop in o)
{
    // name: firstName, value: Joan, type: string
    // name: age, value: 31, type: number
    alert("name: " + prop +" ,value: " +o[prop]+
          " ,type: " + typeofo[prop]);
}

Functions

The code below confirms that functions are indeed objects in JavaScript
function say(name){
   alert("Hello " + name);
}

alert(typeof say);             // => function
alert(say instanceofObject);  // => true

say.volume ="high";
alert(say.volume);            // => high

one method to this:
function Book(title,author) {
   
    this.title = title;                      // book properties
    this.author = author;
   
    this.details = function(){              // book method 
        returnthis.title +" by " +this.author;
    }
}

In the code below a new Book instance is created and we invoke its detailsmethod:

varbook = newBook("Ulysses","James Joyce");

alert(book.details());        // => Ulysses by James Joyce
JavaScript is a prototype-based language:

varBook =function(author){
    this.author = author;
};

alert(Book.prototype);       // => [object Object], so there is something

Here is an example:

function Rectangle(width,height) {
    this.width = width;
    this.height = height;
}

Rectangle.prototype.area = function() {
    returnthis.width *this.height;
};

var r1 =new Rectangle(4,5);  
var r2 =new Rectangle(3,4);  
alert(r1.area());               // => 20
alert(r2.area());               // => 12

The number variable type

The implication of this is that in JavaScript the values 10, 10.0, and 1e1 are all the same.
var a =10;    
var b =10.0;
var c =1e1;
alert(a ===b);     // => true
alert(a ===c);     // => true
alert(b ===c);     // => true

The string variable type

you can easily use a single character string, such, as "a", or "Y". Here are some string examples:
var s = "Hello World";
var t =s.substr(6);      // new string
alert(t);                 // => World
The Boolean variable type

Like in other languages, JavaScript's Boolean has two possible values: true and false. Note that true and false are language keywords and they are distinct from 1 and 0.
var b =false;
alert(b);                // => false (i.e. not 0)

null and undefined

When your function has no return value, it returns undefined. If you declare a variable and don't initialize it, it returns the undefined value. If you query a non-existent array element or object property, again an undefined is returned. Here is an example.
var book;          
alert(book);          // => undefined
alert(typeof book);   // => undefined

If you want to indicate the 'lack of value' in your code, you typically use null rather than undefined.
var book =null; 
alert(book);          // => null
alert(typeof book);   // => object  (although null is not a true object)

if statement

Here is a simple example:

var person ={ age:33 };

if (person.age >= 18){
    alert ("Adult");             // => Adult
    alert ("Allowed to vote");   // => Allowed to vote 
}

They are separated by an || (or) operator:

vara = 4;
var b =5;

if (a <= 7|| b >10) {   // true
    alert("yes");         // => yes
}

if…else statement

The if-statement may contain an optional else clause that specifies an alternative course of action. The else clause is executed if the expression in the if-statement is evaluated to false.
var password ="secret";
if (password.length >= 7){
   alert("okay");
} else{
   alert("Number of characters in your password must be at least 7.");
   returnfalse;
}

If no else-if condition is evaluated to true, the statements inside the else block are executed.
var age =34;
if (age < 13){
    alert("child");        // => child
} elseif (age < 19){
    alert("adolescent");   // => adolescent
} else{
    alert("adult");        // => adult
}

switch statement

Here is an example:
var account =3;
switch (account){
   case1:
      alert("Checking account");   // => Checking account
      break;
   case2:
      alert("Savings account");    // => Savings account
      break;
   case3 :
      alert("Business account");   // => Business account
      break;
   default:
      alert("Invalid account code");
      break;
}

Avoid switch fall-through

You should end each case with an explicit break statement. If a break is absent, case statements 'fall through' meaning that the control will flow sequentially through subsequent case statement.
var account =3;
switch (account){
   case1:
      alert("Checking account");   // => Checking account 
      break;
   case2:
      alert("Savings account");    // => Savings account
      break;
   case3:
      alert("Business account");   // => Business account (falls through)
   default:
      alert("Invalid account code");
      break;
}

while loop

Here is an example of a JavaScript while loop:
var sum =0;
var number =1;
while (number <= 50){  // -- condition
  sum +=number;        // -- body
  number++;             // -- updater
}
alert("Sum = " +sum);  // => Sum = 1275

do-while loop

Here is an example of a JavaScript do-while loop:
var sum =0;
var number =1;
do {
   sum +=number;         // -- body
   number++;              // -- updater
} while(number <=50);   // -- condition
alert("Sum = " +sum);    // => Sum = 1275

for loop

The most frequently used loop in JavaScript is the for-loop. Here is an example:
var sum =0;
for (vari = 1;i <= 50;i++) {
   sum =sum + i;
}
alert("Sum = " +sum);    // => Sum = 1275

for-in loop

A for-in loop iterates through the properties of an object and executes the loop's body once for each enumerable property of the object. Here is an example:
var student ={ name:"Bill",age: 25,degree: "Masters"};
for (varitem in student){
   alert(student[item]);     // => "Bill", then 25, then "Masters"
}

An easy way to skip properties and functions that are not part of the object itself use the built-in hasOwnProperty method.
var Student= function(name){
    this.name = name;
}
Student.prototype.age = 38;

var student =new Student("Carl");

for (varitem in student){
   if(student.hasOwnProperty(item)){
       alert (student[item]);         // => Carl. age is not displayed
   }
}

break statement

When JavaScript encounters a break statement in a loop it immediately exits the loop without executing any other statements in the loop. Control is immediately transferred to the statement following the loop body. Here is an example:
var sum =0;
for (vari = 1;i <= 10000;i++) {
   sum +=i;
   if(i ===50) {
       break;    // immediately transfers control outside the for block
   }
}
alert("Sum = " +sum);       // => Sum = 1275

Run

When an infinite loop is created intentionally, you can use a break statement to controls termination of the loop, like so:
var number =1;
var sum =0;
while (true)    // equivalent to for ( ; ; ), called 'forever' loop
{
    sum +=number;
    if(number ===50) {
        break;  // immediately transfers control outside while block
    }
    number++;
}
alert("Sum = " +sum);       // => Sum = 1275       

Run

The number++;statement won't be executed when the loop is entered for the 50th time.

continue statement

When JavaScript encounters a continue statement in a loop it stops the execution of the current iteration and goes back to the beginning of the loop to begin the next iteration. The example below displays only even numbers.
for (vari = 1;i <= 10;i++)
{
   if((i %2) !=0) {
      continue;
   }
   alert(i);           // => 2, 4, 6, 8, 10
}

Run

The continue statement can also be used in other loops. However, in a for-loop it behaves differently from when used in a while loop. In the example above, the for-loop first evaluates the i++ expression and then tests the i <= 50 condition. Now, consider the while loop:
var number =0;

while (number <= 10){
   number++;
   if((number %2) !=0) {
       continue;
   }

   alert(number);     // => 2, 4, 6, 8, 10
}

value types and reference types:

var x = 1;
var y = x;      
alert(x == y);    // => true
alert(x === y);   // => true
x = 6;            
alert(x);         // => 6 
alert(y);         // => 1
alert(x == y);    // => false
alert(x === y);   // => false

When variable y is assigned to x it copies its value and following the assignment any relationship between x and y is severed. So, changing the value of x has no impact on the value of y.Consider this example where a reference type is copied:
var x ={ make:"Toyota" };
var y =x;
alert(x ==y);      // => true
alert(x ===y);     // => true
x.make ="Ford";
alert(x.make);      // => Ford
alert(y.make);      // => Ford
alert(x ==y);      // => true
alert(x ===y);     // => true

Here are some examples of string literals:

var s1 ="Don't ignore Peter's feedback";
var s2 ='Don\'t ignore Peter\'s feedback';

var s3 ='Andrew Fuller\n Bob Springsteen';
var s4 ="Andrew Fuller, \
Bob Springsteen, \
Helena Williams";

alert(s1);
alert(s2);
alert(s3);
alert(s4);

Run

Note that using the continuation character is generally not recommended.

Here are some other string members you frequently use: length, and charAt.

var s ="Paris, London, Amsterdam";

alert(s.length);              // => 24
alert(s.charAt(0));           // => P. First character
alert(s.charAt(s.length-1));  // => m. Last character

And here are some additional frequently used string methods: indexOf, lastIndexOf, toLowerCase, substring, replace, and split.
var s ="Paris, London, Amsterdam";
// Gets position of first 'a', returns 1
alert(s.indexOf("a"));       
// Gets position of first 'a' starting at 3, returns 22
alert(s.indexOf("a",3));    
// Gets position of last 'o', returns 11
alert(s.lastIndexOf("o"));    
// Converts string to lower-case
alert(s.toLowerCase());      
// Gets substring starting from the 15th character to the last,
alert(s.substring(14,s.length));
// Replaces "London" with "Berlin"
alert(s.replace("London","Berlin"));  
// splits into an array of substrings using ", " separator
alert("Array: " +s.split(", "));

When comparing two strings they are considered equal when they have the same length and the same sequence of characters in corresponding positions.
var str1 ="Hello World";
var str2 ="Hello" +" World";
alert(str1 ==str2);      // => true
alert(str1 ===str2);     // => true

Here are some examples of string literals:

var s1 ="Don't ignore Peter's feedback";
var s2 ='Don\'t ignore Peter\'s feedback';

var s3 ='Andrew Fuller\n Bob Springsteen';
var s4 ="Andrew Fuller, \
Bob Springsteen, \
Helena Williams";

alert(s1);
alert(s2);
alert(s3);
alert(s4);

Run

Note that using the continuation character is generally not recommended.

Here are some other string members you frequently use: length, and charAt.

var s ="Paris, London, Amsterdam";

alert(s.length);              // => 24
alert(s.charAt(0));           // => P. First character
alert(s.charAt(s.length-1));  // => m. Last character

Run

And here are some additional frequently used string methods: indexOf, lastIndexOf, toLowerCase, substring, replace, and split.

var s ="Paris, London, Amsterdam";

// Gets position of first 'a', returns 1
alert(s.indexOf("a"));       

// Gets position of first 'a' starting at 3, returns 22
alert(s.indexOf("a",3));    

// Gets position of last 'o', returns 11
alert(s.lastIndexOf("o"));   

// Converts string to lower-case
alert(s.toLowerCase());      

// Gets substring starting from the 15th character to the last,
alert(s.substring(14,s.length));

// Replaces "London" with "Berlin"
alert(s.replace("London","Berlin"));  
// splits into an array of substrings using ", " separator
alert("Array: " +s.split(", "));

When comparing two strings they are considered equal when they have the same length and the same sequence of characters in corresponding positions.
var str1 ="Hello World";
var str2 ="Hello" +" World";
alert(str1 ==str2);      // => true
alert(str1 ===str2);     // => true

The Boolean type has two literal values: true and false:

varempty = "";
alert(Boolean(empty));            // => false
var nonEmpty ="JavaScript is cool!";
alert(Boolean(nonEmpty));         // => true

Automatic conversions to Boolean equivalents are common in conditional statements.
var car ={ make:"Toyota" };
var display =true;
if (car && display){        // => true
    alert(car.make);
}
car = null;
if (car){                  // => false
   alert("drive my car");
}