注：我对原文进行了编辑，对一些词汇标注颜色，方便阅读。本来准备翻译，但是觉得文章简单易懂，而且原文写得很好，所以就不献丑了。希望对JavaScript初学者能有所帮助。你可以跟着作者一起做那些示例代码，等读完文章的时候，你就可以掌握JavaScript的基本操作了，你会发现其实这一切很容易。
Contents
Embedding and including
write and writeln
Document object
Message box
Function
Event handler
Form
Link
Date
Window
Frame
Embedding and including
Let's first see a simple example:
< html >< head >
< title > ThisisaJavaScriptexample title >
< script language ="JavaScript" >
script >
head >
< body > Hi,man! body >
html >
Usually, JavaScript code starts with the tag . The code placed between
and . Sometimes, people embed the code in the tags: < html >< head > head >
< body >
< script >
.. // Thecodeembeddedinthetags. script >
body >
html >
Why do we place JavaScript code inside comment fields ?
It's for ensuring that the Script is not displayed by old browsers that do not support JavaScript. This is optional, but considered good practice. The LANGUAGE attribute also is optional, but recommended. You may specify a particular version of JavaScript:
You can use another attribute SRC to include an external file containing JavaScript code:
< script language ="JavaScript" src ="hello.js" > script >For example, shown below is the code of the external file hello.js:
document.write("HelloWorld!")The external file is simply a text file containing JavaScript code with the file name extension ".js".
Note:
Including an external file only functions reliably across platforms n the version 4 browsers. The code can't include tags , or you will get an error message.write and writeln
In order to output text in JavaScript you must use write() or writeln(). Here's an example:
< HTML >< HEAD >
< TITLE > Welcometomysite TITLE > HEAD >
< BODY >
< SCRIPT LANGUAGE ="JAVASCRIPT" >
SCRIPT >
BODY >
HTML >
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.
Document object
The document object is one of the most important objects of JavaScript. Shown below is a very simple JavaScript code:
document.write("Hithere.")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
You can always include the last update date on your page by using the following code:
< script language ="JavaScript" >
document.write( " ThispagecreatedbyJohnN.Lastupdate: " + document.lastModified);
script >
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.write.
bgColor and fgColor
Lets try playing around with bgColor and fgColor:
< script >
document.bgColor = " black "
document.fgColor = " #336699 "
script >
Message Box
alert
There are three message boxes: alert, confirm, and prompt. Let's look at the first one:< body >
< script >
window.alert( " Welcometomysite! " )
script >
body >
You can put whatever you want inside the quotation marks.
confirm
An example for confirm box:window.confirm("Areyousureyouwanttoquit?")
prompt
Prompt box is used to allow a user to enter something according the promotion:window.prompt("pleaseenterusername")
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()
Variables and Conditions
Let's see an example:
< script >var x = window.confirm( " Areyousureyouwanttoquit " )if (x)
window.alert( " Thankyou. " )
else
window.alert( " Goodchoice. " )
script >
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.
< script >var y = window.prompt( " pleaseenteryourname " )
window.alert(y)
script >
Another example:
< html >< head >< script >
var x = confirm( " Areyousureyouwanttoquit? " )
if ( ! x)
window.location = " http://www.yahoo.com "
script >
head >
< body >
Welcometomywebsite!.
body > html >
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".
Function
Functions are chunks of code.Let's create a simple function:
{
document.write("Hellocanyouseeme?")
}
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:
{
document.write("Hellocanyouseeme?")
}
test()
Last line test() calls the function, now you will see the words "Hello can you see me?".
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
onClick handlers execute something only when users click on buttons, links, etc. Let's see an example:
< script >
function ss()
{
alert( " Thankyou! " )
}
script >
< form >
< input type ="button" value ="Clickhere" onclick ="ss()" >
form >
The function ss()is invoked when the user clicks the button. Note: Event handlers are not added inside the