CS 330 Class 5

1
CS 330 Class 5

• Programming plan for today
• More on types (Flanagan Ch 3, 11.1)
• Dialog boxes
• Functions

2
Data Types and Values (Ch. 3)

• Number integer, octal, hex, float inferred from
  the context
• var aNumber 4.5 // no typing, declaration
  optional
• String (3.2)
• Text within single or double quotes.
• onclick"alert('You win a car')
• Exception a literal single quote name Susys
  place
• Concatenation via
• firstname Mary
• name firstname Smith
• Property name.length
• Method name.charAt(0) returns the first letter
• See p. 518 for other string features

3
Type Conversion (CH 11.1)

• Automatic JavaScript will attempt to convert
  values to the type needed in a context.
• Try the following.
• javascriptalert(hello 5), alert(35),
  alert(35)
• Explicit (good examples on p. 165-6)
• parseInt(aString) returns an integer at the
  beginning of aString
• parseFloat(aString) returns a float
• Return to add.htm.
• We need parseint becauase form variables are all
  text.

4
JavaScript is Object-Based

• Objects (document, forms,) have properties,
  methods, and events
• Properties (values associated with an object)
• theForm.theSum.value in add.htm
• The object is theForm.theSum, the property is
  value
• aString.length
• The object is aString, the property is
  length
• Methods (something done with respect to an
  object)
• document.write(ltbrgtHello there)
• The object is document, the method is write
• Events
• onclick alert(You got my goat) in alert2.htm
  is triggered by the users action. The object is
  button, the event is alert.

5
Dialog Boxes (Pop-Ups)

• Three types alert, confirm, prompt.
• They can be triggered
• In an event handler alert2.htm.
• Flanagan p 353 lists events that can
  trigger dialogs
• 2. By code embedded in ltscriptgt tags
  confirm.htm, prompt.htm.
• Different open another window. This returns no
  information to the page.
• Caveat pop-ups can be annoying. Use only when
  needed.

6
Functions

• Putting an alert in a functionfn1.htm
• Adding a parameter fn2.htm, fn3.htm
• More than one parameter fn4.htm
• Returning a value fn5.htm
• Recursion fn6.htm
• More complex programming count.htm