Chaining a variable number of asynchronous tasks with JQuery promises (http://jsfiddle.net/qopu5vLL/)

chaining-asynchronous-tasks

$(function() {

    function doChainedTasks(tasks) {
        var promise = tasks[0]();
        var results = [];
        $.each(tasks.slice(1), function(i, task) {
            promise = promise.then(function(value) {
                results.push(value);
                return task();
            });
        });
        promise.then(function(value) {
            results.push(value);
            println("All Results -> " + results);
        });
    }
    
    
    function a() {
        var dfr = $.Deferred();
        setTimeout(function() {
            println("Function a() finished");
            dfr.resolve("Result a");
        }, 500);
        return dfr.promise();
    }
    
    function b() {
        var dfr = $.Deferred();        
        setTimeout(function() {
            println("Function b() finished");
            dfr.resolve("Result b");
        }, 1500);
        return dfr.promise();
    }

    function c() {
        var dfr = $.Deferred();
        setTimeout(function() {
            println("Function c() finished");
            dfr.resolve("Result c");
        }, 2000);
        return dfr.promise();
    }
    
    function println(msg) {
        $("body).append(msg + "<br/>");
    }
    
    var tasks = [a, b, c]
    
    doChainedTasks(tasks);

});