Building iPhone Apps with HTML, CSS, and ... - Cdn.oreilly.com

• Array keys are assigned beginning at 0.
• The single equals sign is the assignment operator.
• The double equals sign is the equivalence logical operator.
• The plus sign is the string concatenation operator.
For our purposes, the most important feature of JavaScript is that it can interact with
the elements of an HTML page (the cool kids call this “manipulating the DOM”).
Example 1-9 shows a simple bit of JavaScript that changes some text on the page when
the user clicks on the h1.
DOM stands for Document Object Model, and in this context it represents
the browser’s understanding of an HTML page. You can read more
about the Document Object Model here: http://en.wikipedia.org/wiki/
Document_Object_Model.
Example 1-9. Simple OnClick handler
My Awesome Page
function sayHello() {
document.getElementById('foo').innerHTML = 'Hi there!';
}
Click me!
Here’s an explanation:
I’ve added a script block to the head of the HTML document.
Inside the script block, I’ve defined a single JavaScript function named sayHello().
The sayHello() function contains a single statement, which tells the browser to “look
through the document for an element that has the id ‘foo’, and set its innerHTML
contents to ‘Hi there!.’” The effect of this in the browser is that the text “Click me!”
will be replaced with “Hi there!” when the user clicks on the h1 element.
End of the sayHello() function.
End of the script block.
The onclick attribute of the h1 element tells the browser to do something when the
user clicks on the h1, namely, to run the sayHello() function.
10 | Chapter 1: Getting Started