国外的为初学者写的JavaScript教程_基础知识

You can use another attribute SRC to include an external file containing JavaScript code:

For example, shown below is the code of the external file hello.js:

document.write("Hello World!")

The external file is simply a text file containing JavaScript code with the file name extension ".js". Note:

1. Including an external file only functions reliably across platforms in the version 4 browsers.
2. The code can't include tags , or you will get an error message.

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write and writeln

In order to output text in JavaScript you must use write() or writeln(). Here's an example:

Note: the document object write is in lowercase as JavaScript is case sensitive. The difference between write and writeln is: write just outputs a text, writeln outputs the text and a line break.

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Document object

The document object is one of the most important objects of JavaScript. Shown below is a very simple JavaScript code:

document.write("Hi there.")

In this code, document is the object. write is the method of this object. Let's have a look at some of the other methods that the document object possesses.

lastModified

All you need to do here is use the lastModified property of the document. Notice that we used + to put together This page created by John N. Last update: and document.lastModified.

bgColor and fgColor

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Message Box

alert

You can put whatever you want inside the quotation marks.

confirm

 
window.confirm("Are you sure you want to quit?") 

prompt

 
window.prompt("please enter user name") 

In all our examples above, we wrote the box methods as window.alert(). Actually, we could simply write the following instead as:

alert() 
confirm() 
prompt()

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Variables and Conditions

Let's see an example:

There are several concepts that we should know. First of all, var x= is a variable declaration. If you want to create a variable, you must declare the variable using the var statement. x will get the result, namely, true or false. Then we use a condition statement if else to give the script the ability to choose between two paths, depending on this result (condition for the following action). If the result is true (the user clicked "ok"), "Thank you" appears in the window box. If the result is false (the user clicked "cancel"), "Good choice" appears in the window box instead. So we can make more complex boxes using var, if and those basic methods.

Another example:

 
 
 
 
Welcome to my website!. 

If you click "cancel", it will take you to yahoo, and clicking ok will continue with the loading of the current page "Welcome to my website!". Note:if (!x)means: if click "cancel". In JavaScript, the exclamation mark ! means: "none".

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Function

Functions are chunks of code.Let's create a simple function:

function test() 
{ 
 document.write("Hello can you see me?") 
}

Note that if only this were within your tags, you will not see "Hello can you see me?" on your screen because functions are not executed by themselves until you call upon them. So we should do something:

function test() 
{ 
 document.write("Hello can you see me?") 
} 
test() 

Last linetest() calls the function, now you will see the words "Hello can you see me?".

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Event handler

What are event handlers? They can be considered as triggers that execute JavaScript when something happens, such as click or move your mouse over a link, submit a form etc.

onClick

The function ss() is invoked when the user clicks the button. Note: Event handlers are not added inside the tags, but rather, inside the html tags.

onLoad

onMouseover,onMouseout

Over Here! 
Get Out Here!

onUnload

Handle multiple actions

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Form

Let's say you have a form like this:

Notice that we gave the names to the form and the element. So JavaScript can gain access to them.

onBlur

 
Email:
 
Comment: 
 
 
 

If you enter an email address without the @, you'll get an alert asking you to re-enter the data. What is: x.indexOf(@)==-1? This is a method that JavaScript can search every character within a string and look for what we want. If it finds it will return the position of the char within the string. If it doesn't, it will return -1. Therefore, x.indexOf("@")==-1 basically means: "if the string doesn't include @, then:

alert("It seems you entered an invalid email address.") 
document.feedback.email.focus()

What's focus()? This is a method of the text box, which basically forces the cursor to be at the specified text box. onsubmit Unlike onblur, onsubmit handler is inserted inside the

Note:
if(document.login.userName.value==""). This means "If the box named userName of the form named login contains nothing, then...". return false. This is used to stop the form from submitting. By default, a form will return true if submitting. return validate() That means, "if submitting, then call the function validate()".

Protect a file by using Login

 
 
function checkLogin(x) 
{ 
if ((x.id.value != "Sam")||(x.pass.value !="Sam123")) 
{ 
 alert("Invalid Login"); 
 return false; 
} 
else 
 location="main.htm" 
} 

 
 
UserID:
 
Password:
 
 
 

|| means "or", and ,!= indicates "not equal". So we can explain the script: "If the id does not equal 'Sam', or the password does not equal 'Sam123', then show an alert ('Invalid Login') and stop submitting. Else, open the page 'main.htm'".

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Link

In most cases, a form can be repaced by a link:

Click to reload!

More examples:

Click me to say Hello

Mouse over to see Main Page

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Date

Let's see an example:

 
 
 
var x= new Date(); 
document.write (x); 
 

To activate a Date Object, you can do this: var x=new Date(). Whenever you want to create an instance of the date object, use this important word: new followed by the object name().

Dynamically display different pages

var banTime= new Date() 
var ss=banTime.getHours() 
if (ss<=12) 
 document.write("") 
else 
 document.write("") 

Window

Open a window

You can replace test.htm with any URL, for example, with http://www.yahoo.com.

Size, toolbar, menubar, scrollbars, location, status

open("URL","name","attributes")

For example:

Another example with no attributes turned on, except the size changed:

Here is the complete list of attributes you can add:

Reload

window.location.reload()

Close Window

 
 
 
Close Window

Loading

window.location="test.htm"

This is the same as

aa=window.open('test.htm','','width=200,height=200')

 
 
 
 
 
 
File 
1
 
File 
2
 
 

Try it now!

One of the most popular uses of loading multiple frames is to load and change the content of more than one frame at once. Lets say we have a parent frame:

We can add a link in the child frame "frame1" that will change the contents of not only page1, but page2 too. Shown below is the html code for it:

 
 
 
This is page 1 
 
Click Here 
 

Notice: You should use "parent.frameName.location" to access another frame. "parent" standards for the parent frame containing the frameset code.