Basic JavaScript tutorial
I'd like to start by saying I don't like JavaScript. I'd just like to introduce anyone who is interested to very basic concepts in JavaScript. All the code I will post will be tested, so if you do something and it doesn't work, it's YOUR fault, not mine.
For your first lesson, let's make an "alert" dialog box.
Open up notepad and type:
<html><head>
<title>First JavaScript lesson: Alert Boxes.</title>
<script language="JavaScript">
alert("This is an alert dialog box.");
</script></head>
<body></body></html>
Save it as *.htm or *.html, and open it in a web browser, needless to say, JavaScript must be enabled.
For your second lesson we're going to go into a slightly more advanced sort of dialog box, the prompt dialog box.
Open up notepad and type:
<html><head>
<title>Second JavaScript lesson: Prompt Boxes.</title>
<script language="JavaScript">
prompt("This is a Prompt dialog box.","This is where you get input from users");
</script></head>
<body></body></html>
Again, save as *.htm or *.html and open in a web browser.
Now for some learning. For your third lesson, we'll be taking input from a prompt dialog box and responding to it with an alert dialog box using an if, then, else loop which is a staple in any programming language.
Open up notepad and type:
<html><head>
<title>Third lesson: The if, then, else loop.</title>
<script language="JavaScript">
var input = prompt("Please type 'yes'","");
if ( input == "yes" )
{
alert("Thank you for typing 'yes'.");
}
else if (input == "no" )
{
alert("That's not what I asked for.");
}
else
{
alert("I don't understand.");
}
</script></head>
<body></body></html>
Now I'm going to break this one down as it looks a little "codey" and may be daunting to those who do not understand. First, we ask a user to type "yes" (case sensitive) and if they do, they will be greeted with "Thank you", and if they type "no" they will be greeted with a different message, for any other message or input, or any case insensitive input we didn't include an option for they program will say "I don't understand." Please note that the semicolon is not technically necessary, however it is good practice if you wish to move on to C++ where semicolons are necessary. First we declare a variable which in JavaScript is done by typing "var" and then a variable name which cannot start with, but may contain numbers. You may have noticed that when we are checking the contents of the variable we test it with an "if" statement and use two "=" signs, this is basically saying, if the variable is exactly equal to "text", then carry out the actions in the "{}", otherwise move on to the next step. Next we have an "else if" statement, which I find useful because JavaScript is kinda buggy if you use the or operator which is "||" in JavaScript, we'll get into operators later. Then there is the generalized "else" statement which is basically saying if the input did not meet the above requirements, perform this function.
Moving on to operators.
I'm only going to cover a few operators here, the basics are as follows:
Exactly equal ==
Not equal !=
Or ||
and &&
You may see these used throughout the tutorial, although the most common will be == and !=.
Now for the fourth lesson, converting strings to integers. (Used here to make a simple calculator.)
Open up notepad and type:
<html><head>
<title>Fourth lesson: Converting strings to integers for calculations.</title>
<script language="JavaScript">
var num1 = prompt("Insert first number.","");
var num2 = prompt("Insert second number.","");
var handle = prompt("Insert method of calculation.","+,-,*,/");
var answer;
if ( handle == "+")
{
answer = num1/1 + num2/1;
}
else if ( handle == "-")
{
answer = num1/1 - num2/1;
}
else if ( handle == "*" )
{
answer = num1/1 * num2/1;
}
else if ( handle == "/" )
{
answer = num1/1 / num2/1;
}
else
{
alert("I do not understand.");
}
</script></head>
<body>
<script language="JavaScript">
document.writeln(answer);
</script></body></html>
Okay, so basically what we did was divide the all the variables by 1 to make them integers and calculable, if we didn't do this, 1 + 1 would equal 11 because it would add the strings instead of the numbers. There may be a way to declare integers in JavaScript, but hey, I'm lazy and all this crap is off the top of my head. The only really new stuff here is the "document.writeln(answer);" argument, which tells JavaScript to write the variable "answer" to the HTML document. For instance if you prompted "Enter your name" and wrote that variable to the HTML document, the user's name would appear on the page.
Now for you fifth and final lesson in JavaScript (from me anyhow) we're going to learn how to get information from HTML inputs inside forms (I say from inside forms because it's easy if you have multiple forms and fields.) and use that information. And as before we're going to make a calculator, however this one will be slightly more sophisticated. I only like making calculators because it's a practical use and it's easy. This lesson will introduce you to functions and I'm sorry it may be a tad complicated to those not familiar with the concept.
The only thing you have to remember is:
Window.Document.FormName.InputName.Value.
Open up notepad and type:
<html><head>
<title>Fifth lesson: using information from forms and fields.</title>
<script language="JavaScript">
var answer;
function onplus()
{
answer = window.document.form1.firstnum.value/1 + window.document.form1.secondnum.value/1;
window.document.form1.answer.value = answer;
}
function onminus()
{
answer = window.document.form1.firstnum.value/1 - window.document.secondnum.value/1;
window.document.form1.answer.value = answer;
}
function ontimes()
{
answer = window.document.form1.firstnum.value/1 * window.document.form1.secondnum.value/1;
window.document.form1.answer.value = answer;
}
function ondivide()
{
answer = window.document.form1.firstnum.value/1 / window.document.form1.secondnum.value/1;
window.document.form1.answer.value = answer;
}
</script></head>
<body>
<form name="form1">
<input type="text" name="firstnum" value="" ><br>
<input type="text" name="secondnum" value=""><br>
<input type="text" name="answer" value=""><br>
<input type="button" name="add" value="+" onClick="onplus()";>
<input type="button" name="subtract" value="-" onClick="onminus()";><br>
<input type="button" name="multiply" value="*" onClick="ontimes()";>
<input type="button" name="divide" value="/" onClick="ondivide()";><br>
</form></body></html>
I apologize upfront for the abrupt introduction to functions. Basically a function is something that can be called upon later. There are handlers for functions they are:
onClick
onSubmit
onMouseOver
Try playing around with the various handlers for JavaScript functions (I don't recommend onSubmit for this type of app.) they basically do what the name suggests and have a variety of uses when properly coded into a JavaScript application. If you want you can add a "pi" button by using the function code:
function onpi()
{
answer = window.document.form1.firstnum.value/1 * 3.1415926535;
window.document.form1.answer.value = answer;
}
and the button code:
<input type="button" name="pime" value="Multiply first number by pi." onClick="onpi()";>
If there's any part of this tutorial you do not understand, I apologize, but in my defense, it is two in the morning. Thank you for reading this.
EDIT: Tomorrow I may update with "while", and "for" loops.
That's right, I'm back with a few more things I'd like to add to this tutorial, first I'll start with while loops. A while loop is basically declared like this:
while ( variable != other variable)
{
Do this stuff;
}
Pop open notepad and type:
<html><head>
<title>Lesson six: The while loop.</title>
<script language="JavaScript">
var key = "password";
var guess;
while ( guess != key )
{
guess = prompt("Only by typing 'password' may you continue.","");
}
</script></body</html>
As you can see, we've made an uber-basic password protected page so to speak. The while loop will continue to loop forever and ever until it gets what it wants, for example if we said var key = 1 and var guess = 1 and then declared while ( key != guess ) { alert("Fail."); } it would alert "fail" forever. Moving on to for loops.
Open up notepad and type:
<html><head>
<title>Lesson seven: For loops, making your browser count.</title>
<script language="JavaScript">
for ( i = 1; i <= 1000; i++ )
{
document.writeln(i);
}
</script></head><body>
</body></html>
When you load this page, it will display the numbers 1-1000 on the page, you can play around with the for loop on your own time.
Well I think I'm going to add relocating the browser.
Open notepad and type:
<html><head>
<title>Lesson eight: Location.href.</title>
<script language="JavaScript">
function go()
{
location.href="http://www.google.com/";
}
</script></head>
<body>
<input type="button" name="googler" value="Visit www.Google.com" onMouseOver="go()";>
</body></html>
This was an example of a simple JavaScript re-direct. You can also use a user's input to redirect them locally or anywhere on the internet using this code:
<html><head>
<title>Lesson eight-and-one-half: user defined re-direct.</title>
<script language="JavaScript">
function go()
{
location.href = window.document.form1.url.value;
}
</script></head>
<body><form name="form1">
<input type="text" name="url" value="http://">
<input type="button" name="goto" value="Visit URL" onClick="go()";>
</form></body></html>
This is an example of a simple user operated re-direct script. If you know what you're doing, you can even load web pages into different frames. I don't have an example off hand, however.
dow. Check your history. It will say Google.com.