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

you are the person driving, in which case it could take considerably longer (did I say
“crash” course?).
Intro to JavaScript
At this point you should know how to structure a document with HTML and how to
modify its visual presentation with CSS. Now we’ll add some JavaScript to make it do
stuff.
JavaScript is a scripting language that can be added to an HTML page to make it more
interactive and convenient for the user. For example, you can write some JavaScript
that will inspect the values typed in a form to make sure they are valid. Or you can have
JavaScript show or hide elements of a page depending on where the user clicks.
JavaScript can even contact the web server to execute database changes without refreshing
the current web page.
Like any modern scripting language, JavaScript has variables, arrays, objects, and all
the typical control structures (if, while, for, and so on). Example 1-8 shows a snippet
of JavaScript that illustrates several core concepts of the language.
Example 1-8. Basic JavaScript syntax
var foods = ['Apples', 'Bananas', 'Oranges'];
for (var i in foods) {
if (foods[i] == 'Apples') {
alert(foods[i] + ' are my favorite!');
} else {
alert(foods[i] + ' are okay.');
}
}
Here’s an explanation of what’s happening here:
Define an array named foods that contains three elements.
Open a for loop that defines a variable named i that will contain the index of each
element of the array during the loop.
A garden-variety if checks to see if the current element of the array is equal to Apples.
This is displayed if the current element of the array is equal to Apples.
This is displayed if the current element of the array is not equal to Apples.
Here are some points about JavaScript’s syntax that are worth noting:
• Statements are terminated with semicolons.
• Code blocks are enclosed in curly braces.
• Variables are declared using the var keyword.
• Array elements can be accessed with square bracket notation.
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