JavaScript

1
JavaScript

• Conditional Repetition Statements

2
Conditional Statement

• if..else statement
• if (condition)
• statement1
• else
• statement2

Multiple statements must be enclosed in braces
Example1
Example2
3
Example 1

• ltSCRIPT LANGUAGE"JavaScript"gt
• var RandNum Math.round(Math.random()100) 1
• document.write(RandNum)
• if (RandNum 2 0)
• document.write(' is even.')
• else
• document.write(' is odd.')
• lt/SCRIPTgt

The math object can be used to generate a random
number
4
Example 2

• ltSCRIPT LANGUAGE"JavaScript"gt
• var Password "Sesame Street"
• var UserEntry
• UserEntry window.prompt("Please enter the
  password")
• if (UserEntry Password)
• window.alert("That's right! Come on in!")
• else
• window.alert("Sorry! You didn't get it right!")
• document.write("The password was ", Password)
• lt/SCRIPTgt

5
For Loop

• A for loop repeats a loop until a specified
  condition evaluates to false.
• for (initial expression condition increment)
• statements

Example
6
Example

• function CountByOnes()
• for (var x 1 xlt10 x)
•    
•     document.write(x)
•                             

Note Curly braces start and end the function
and they also start and end the for loop.
7
While Loop

• A while statement repeats a loop as long as a
  specified condition evaluates to true.
• while(condition)
• statements

Loop
Loop
Loop
Example1
Example2
8
Example1

• ltSCRIPT LANGUAGE"JavaScript"gt
• var count 1
• while (count lt 10)
• document.write(count, 'ltbrgt')
• count
• lt/SCRIPTgt

9
Example2

• ltSCRIPT LANGUAGE"JavaScript"gt
• var UserEntry
• while (UserEntry ! "MFHS")
• UserEntry window.prompt("Please enter 'MFHS'
  ")
• document.write("Excellent! You entered 'MFHS' ")
• lt/SCRIPTgt

10
Break Continue

• The break statement terminates the current while
  or for loop and transfers program control to the
  statement following the terminated loop.

• The continue statement terminates execution of
  the block of statements in a while or for loop,
  and continues execution of the loop with the next
  iteration.
• In a while loop, it jumps back to the condition
• In a for loop in jumps to the increment
  expression.

Example
Example
11
Example

• var j 0
• while (j lt 6)
• if (j 3)
• break
• j
• document.write(j)

The program will go to the statement following
the loop
Output 3
12
Example

• var n 0, sum 0
• while (n lt 6)
• n
• if (n 3)
• continue
• sumn
• document.write(sum)

The program will go to the while statement,
increment n and continue.
Output 12
13
Infinite Loops

• An infinite loop is a loop which never ends
  because there is no terminating condition.

ltSCRIPT LANGUAGE "JavaScript"gt var count
1 while (count lt10) document.write(count,
'ltBRgt') lt/SCRIPTgt