JavaScript 101
Now that you’ve learned a bit about JavaScript and why it exists, it’s time to dive in and start creating your first real script.
The <script> Element
Every script starts with a <script> block you slot somewhere into an HTML document. Really, you have only two options:
The <body> section. Put scripts you want your browser to run right away in the <body> section of your HTML. The browser runs your script as soon as it reaches the <script> element. If you put your script at the beginning of the <body> section, your browser processes the script before it displays the page.
Tip
Usually, JavaScript fans put their scripts at the end of the <body> section. That way, you avoid errors that might occur if you use a script that relies on another part of the page, and the browser hasn’t read that section yet. Because browsers read an entire page quickly, these scripts execute almost immediately.
The <head> section. If you place an ordinary script in the <head> section of your HTML document, it runs immediately, before the browser processes any part of the markup. However, it’s more common to use the <head> section for scripts that contain functions (see Functions). Functions don’t run immediately—instead, you summon them when your visitor takes some kind of action on a page, like moving a mouse.
Note
You can place as many <script> blocks in a web page as you want.
A typical script block consists of a series of programming instructions. To get a handle on how these instructions work, consider ...
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