Tuesday, March 01, 2011

Practical example of jQuery 1.5’s deferred.when() and .then()

"“Fun with jQuery Templating and AJAX” by Dan Wellman is a generally interesting article, but I found the code in the “Getting the Data” block especially interesting – see how each get function RETURNS the $.ajax function call, which can then be called inside a when() function, vastly simplifying the workflow (there’s an error in the listed code – getTweets() is supposed to return the ajax function, not simply execute it).

Even more interesting is this pattern, suggested by commenter Eric Hynds (whose blog has now been added to my Google Reader list):

$.when( $.get('./tmpl/person.tmpl'), $.getJSON('path/to/data') )
   .then(function( template, data ){
      $.tmpl( template, data ).appendTo( "#people" );

The deferred.done() and then() methods will take as arguments the results from each function called in the when() function – in order – i.e. the output of the get will map to template, and the output from the getJson will be mapped to data.  This is pretty sweet!

Perhaps a simpler to observe example of the behavior is shown here: - no prize for correct guesses as to the result of this…

/* Hello and World are both treated as resolved deferreds - they 
can be replaced with any function, like a $.get, etc */
$.when( "Hello", "World" ).then(
   function(x, y){ alert(x + " " + y); }

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