Class 25: Lab: Control Structures, Reconsidered

Held Monday, March 6, 2000

Overview

Today's outline does not yet have an overview. Please let me know if you think it should have one.

Question 25 for today's class: How might the control structures you learned yesterday help you write JavaScript applications?

Question 26 for Tuesday's class: What do you consider significant implications of being able to copy JavaScript programs from the Web?

Notes

• Not to stifle your creativity, but I get a lot of email, and when I'm looking for email from my students, I look under their names. If possible, please set your name appropriately when you send email to me. Thanks.

Contents

• Using a JavaScript Code File
• Friday's Examples
• Replacing the Current Document
• Conditionals
• Repetition
• Repetition with setTimeout
• Reflection

Summary

Using a JavaScript Code File

• Put all of your function definitions in a .js file.
• Put the following in the head of your .html file.

  <script language="javascript" src="statusclock.js"></script>
  

• Use calls to the functions as appropriate.
• This structure is required for XHTML (the succesfor to HTML).

Friday's Examples

I've made some simplified versions of Friday's examples available.

• Status-bar Clock: statusclock.js and statusclock.html
• Clock in a button: buttonclock.js and buttonclock.html
• List of links: linklist.html
• Repetition: yellowballs.js and yellowballs.html
• Automatically changing images changeball.js and changeball.html
• Changing images linkball.html

Replacing the Current Document

• A few of you said "I want my button to update the document." Here's how you do it:

  document.clear();
  document.write(...);
  document.close();
  

• See replace.js and replace.html

Conditionals

• What if you want to do different things depending on various settings you've received?
• Use the conditional, which looks like

  if (condition) {
    stuff to do if the condition holds;
  }
  else {
    stuff to do if the condition fails;
  }
  

Repetition

• The most common type of repetition is the for loop.

  for (var = startvalue; var <= endvalue; var++) {
    // Stuff to do
  }
  

• A sample for loop can be found in repetition.ps and repetition.html

Repetition with setTimeout

• We've also seen that it's possible to do a different kind of repetition with setTimeout

Reflection

• What kinds of things can you envision doing with these various options?
• Can we write an interesting game?