JavaScript Loops

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JavaScript Loops
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Loops

• A loop is a block of code that allows you to
  repeat a section of code a certain number of
  times, perhaps changing certain variable values
  each time the code is executed.

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Why loops are useful?

• Loops are useful because they allow you to repeat
  lines of code without retyping them or using cut
  and paste in your text editor.
• They save time and trouble of repeatedly typing
  the same lines of code, but also avoids typing
  errors in repeated lines.
• You are also able to change one or more variable
  values each time the browser passes through the
  loop.

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For loop
for ( varname1varnamelt11varname1 )
initialization
Tells the loops when to stop running
Determines the rate at which the variable is
changed and whether it gets larger or smaller
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While loop

• A while loop just looks at a short comparison and
  repeats until the comparison is no longer true.
• while(varnamelt11)

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• 1. This is loop 1
• 2. This is loop 2
• 3. This is loop 3
• 4. This is loop 4
• 5. Break the loop !
• 6. This is loop 6
• 7. This is loop 7
• 8. This is loop 8
• 9. This is loop 9
• 10. This is loop 10 Note IF

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Functions
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Function

• Is a JavaScript code that is written to perform
  certain tasks repeatedly

User-defined function

• Is one which the Web developer writes the tasks
  to be performed

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Why functions are useful?

• Helps organize various parts of a script into the
  difference tasks that must be accomplished
• Functions are portable.
• Functions are time-saving.

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Defining the code for functions
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Naming functions

• Function names are case sensitive

• Function name must begin with a letter or an
  underscore character

• Function name cannot contain any spaces

• Avoid reserved words

• Give functions memorable and meaningful names

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Calling functions in your scripts

• A call to a function in JavaScript is simply the
  function name along with the set of parentheses,
  ending with a semicolon, like a normal JavaScript
  statement.

functionname( )
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• lthtmlgt
• ltheadgt
• lt/headgt
• ltbodygt
• ltscript type"text/javascript"gt
• function display_alert()
• alert("")
• display_alert()
• lt/scriptgt
• lt/bodygt
• lt/htmlgt

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• lthtmlgt
• ltheadgt
• ltscript type"text/javascript"gt
• function myfunction()
• alert(This is an alert box")
• lt/scriptgt
• lt/headgt
• ltbodygt
• ltformgt
• ltinput type"button" onclick"myfunction()"
  value"Call function"gt
• lt/formgt
• lt/bodygt
• lt/htmlgt

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