SPEAKER 1: Let's implement a web page that allows users to look up stock quotes. Let's suppose first that there exists a file called quote.php, but this could be implemented in most any language, but whose purpose in life is to expect an HTTP get parameter called symbol, the value of which is the symbol of the stock for which you'd like a quote. 

For instance, if we look at this file in my browser, quote.php, notice that I've passed in, already, a symbol of FB, for Facebook. And notice that what has come back is a JSON object with three keys. One's called symbol, one called name, and one called price. The values of which are exactly that from the file in question. 

Now let's turn our attention to the beginnings of some HTML and JavaScript. Here, in ajax-0.html, notice that inside of my page's body I have a form that has an onsubmit attribute, the value of which is quote and return false, thereby specifying that I'd like to call a JavaScript function called quote and then return false. Meanwhile, inside of that form is a symbol whose ID is, quote unquote, "symbol," and then another input whose type is submit that gives me a submission button. 

Meanwhile, inside of my page's head, there is a script tag, the source of which is the URL to jquery, the very popular JavaScript library, and below that is another script tag, inside of which is the beginnings of some JavaScript that I myself will write. This is the quote function that will ultimately be called, and inside of here let's declare a variable called URL, specified that the value of this variable shall be quote.php?symbol=". 

And now let's concatenate onto the end of that initial string whatever symbol the user has presumably typed. Specifically, let's do +$""#symbol thereby specifying that I'd like to get, with jquery from my DOM, the element whose unique identifier, a symbol. Recall that that is simply the text field into which the user is going to type that stock symbol. 

Then let's call val, which is a function or method that will get the value that the user's typed in. And then let's call a jquery function called getJSON, passing in as the first argument that URL, passing in, as the second argument, an anonymous function that expects a single argument. Data, we'll call it. And inside of this anonymous function, we'll simply do alert, and then in parentheses, data.price. If data, after all, is that JSON object with three fields-- symbol, name, and price, by doing data.price I'll get exactly that value. 

Let's now save the file and open it up in a browser. http://localhost/ajax-0.html. Here we have that form. Let's type in FB for Facebook and get quote. And there, then, is Facebook's latest stock price.