test-break-callbacks.js

/**
 * Trying out different code approaches to break out of a 
 * deep callback chain in node.js
 * 
 */
 
/** 
 * TEST #1 - Using a try/catch block
 */ 
(function (throwError) {
    var sys = require('sys'), 
        c = 0,
        action = function (callback) {
            c = c + 1; 
            sys.puts("Test 1, step: " + c); 
            callback(); 
        };
    
    // start the callback chain
    try {
        action(function () {
            action(function () {
                action(function () {
                    
                    /*
                    this will stop the callback chain here. 
                    however, if it is just an error and not an exception 
                    perhaps using a custom error handler would be better
                    
                    See below
                    */
                    if (throwError) {
                        throw new Error("BOOM");
                    }
                    
                    action(function () {
                        sys.puts("Finished! Test #1"); 
                    });
                });
            });
        });
    } catch (err) {
        sys.puts("Caught Exception: " + err.message);
    }    
}(false)); // toggle true/false to throw exception


/** 
 * TEST #2 - using a function error handler 
 */ 
(function (doError) {
    var sys = require('sys'), 
        c = 0,
        action = function(callback) {
            c = c + 1; 
            sys.puts("Test 2, step: " + c); 
            callback(); 
        }, 
        errorHandler = function() {
            sys.puts("In error hander!"); 
        };
    
    // Perform a callback chain
    action(function () {
        action(function () {
            action(function () {
                // Using a decision loop to break out of the chain
                if (doError) {
                    errorHandler(); 
                    return; 
                } else {
                    action(function() {
                        sys.puts("Finished! Test #2");
                    }); 
                }
            }); 
        }); 
    });
}(false)); // toggle true/false to throw exception