Recursion in Real-world Applications
This is a way recursion is used in a real-world web application. The problem is that we need a modular carousel slider for pictures. However we dont have the luxury of a backend system or even admin privileges on the CMS such as SharePoint. Using recursion we can give the carousel widget a path and some other parameters to make it find all the available pictures to display on the carousel.
This features a nice user experience by loading the first few images which gets displayed immediately so the user can look at the slideshow right away without waiting for all the images to download.
JavaScript:
function addImage(path, counter, filetype, start, end) { var src = path + counter + "." + (filetype||"png"); var img = new Image(); img.onload = function() { img.className = "slide"; if ( counter == (start||1) ) { $("#_items").append( "<div class=\"active item\">"+img.outerHTML+"</div>"); } else { $("#_items").append( "<div class=\"item\">"+img.outerHTML+"</div>"); } counter++; addImage(counter, filetype, start, end); }; if ( counter-1 != (end||"noend") ) { img.src = src; } } // trigger with counter at 0, we can shield this by containing the function in another function addImage("http://placehold.it/350x", 0, "png", 1, 350);
Limitations to the widget are:
- It is not fail safe yet so if image 13 is missing it just stops at 12 images (can be fixed with added js to not fail until it reached the end number if end is defined)
- If the user goes back rather than forward then they will have a bad user experience by looping over rather quickly
- Ability to shut off recursion and instead do a callback so it can be consumed by modern web applications (not just CMS)
N.B. You can present slide decks easily in a CMS by capturing them as images and displaying them in the carousel so the user doesn’t have to open additional software to view the slide deck
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