Working with remote data - Build Windows 8 Apps with HTML5 and JavaScript - page 281

Table 11-2 provides a brief explanation of the URL parameters.

TABLE 11-2 Query string parameters for the Flickr public web service

Parameter Description

This parameter can take the value all or any ; and indicates whether any selected photos must
match all or just any of the specified tags.

tagmode

Set this parameter to json if you want to get a JSON response. You can also specify that the call
should return RSS or a variety of other formats as listed here: http://www.flickr.com/services/
feeds/docs/photos_public .

format

In a Windows Store application, this parameter is required and must be set to 1 . You don't need
this parameter if you're calling the Flickr API from within a JavaScript web application. It is a
setting that relates to how the host environment actually places the call to the remote site.

nojsoncallback

You can set this parameter to a comma-separated list of keywords to match appropriate
photos.

tags

As you may have noticed, the flickrApp.Source property is set to a string that contains a
placeholder—the {0} item. In .NET programming, this type of notation is used to format strings
dynamically. The idea is that when the user clicks the Search button, the handler will read the typed
tags and insert them in the URL string, replacing the placeholder.

The {0} notation is common in .NET Windows programming, but it isn't in JavaScript. So you need
to create a helper function that does the replacement. This is interesting because it shows you a
powerful JavaScript technique—manipulating object prototypes.

preparing the Flickr UrL
It is advisable that you create yet another JavaScript file; call it helpers.js . Add a reference to that file
in your default.html file and make sure that the helpers.js reference precedes the flickrApp.js reference.
Here's the initial content for helpers.js :

////////////////////////////////////////////////////////////
// Applies the .NET {n} convention to format strings
//
String.prototype.format = function () {
var theString = this,
count = arguments.length;

while (count--) {
theString = theString.replace(
new RegExp('\\{' + count + '\\}', 'gm'), arguments[count]);
};

return theString;
};