Which Script Runs First?
As you learned in Hour 1, you can actually have several scripts within a Web document: one or more sets of <script> tags, and any number of event handlers. With all of these scripts, you might wonder how the browser knows which to execute first. Fortunately, this is done in a logical fashion:
Sets of <script> tags within the <head> section of an HTML document are handled first. Since these scripts cannot create output in the Web page, it's a good place to define functions for later use.
Sets of <script> tags within the <body> section of the HTML document are executed after those in the <head> section, while the Web page loads and displays. If there is more than one script in the body, they are executed in order.
Event handlers are executed when their events happen. For example, the onLoad event handler is executed when the body of a Web page loads. Since the <head> section is loaded before any events, you can define functions there and use them in event handlers.