向回撥函式傳遞額外的引數

        在呼叫函式中，使用匿名函式中實現需傳遞的引數，再次匿名函式內呼叫回撥函式。

1. var events =require("events");
2. functionCarShow(){
3. events.EventEmitter.call(this);
4. this.seeCar =function(make){
5. this.emit('sawCar', make);
6. }
7. }
8. CarShow.prototype.__proto__ = events.EventEmitter.prototype;
9. var show =newCarShow();
10. function logCar(make
    ){
11. console.log("Saw a "+make);
12. }
13. function logColorCar(make, color){
14. console.log("Saw a %s %s ", color, make);
15. }
16. show.on("sawCar", logCar);
17. show.on("sawCar",function(make){
18. var colors =["red","blue","black","pink","green"];
19. var color = colors[Math.floor(Math.random()*3)];
20. logColorCar(make, color);
21. });
22. show.seeCar("Ferrari");
23. show.seeCar("Porsche");
24. show.seeCar("Bugatti");

在回撥中實現閉包

        如果某個回撥函式需要訪問父函式的作用域的變數，就需要使用閉包，在函式塊內部封裝一個非同步呼叫，並傳入所需要的變數。

1. function logCar(logMsg, callback){
2. process.nextTick(function(){
3. callback(logMsg);
4. });
5. }
6. var cars =["獵豹","捷達","朗逸"];
7. for(var idx in cars){
8. var msg ="Saw a "
   +cars[idx];
9. logCar(msg,function(){
10. console.log("Normal Callback "+ msg);
11. });
12. }
13. for(var idx in cars){
14. var msg ="Saw a "+cars[idx];
15. (function(msg){
16. logCar(msg,function(){
17. console.log("Closure Callback "+ msg);
18. })
19. })(msg);
20. }
21. //Normal Callback Saw a 朗逸
22. //Normal Callback Saw a 朗逸
23. //Normal Callback Saw a 朗逸
24. //Closure Callback Saw a 獵豹
25. //Closure Callback Saw a 捷達
26. //Closure Callback Saw a 朗逸

鏈式回撥

        使用非同步函式時，如果兩個函式都在事件佇列上，則無法保證它們的執行順序。解決方法是讓來自非同步函式的回撥再次呼叫該函式，直到沒有更多的工作要做，以執行鏈式回撥。

1. function logCar(car, callback){
2. console.log("Saw a %$", car);
3. if(cars.length){
4. process.nextTick(function(){
5. callback();
6. });
7. }
8. }
9. function logCars(cars){
10. var car = cars.pop();
11. logCar(car,function(){
12. logCars(cars);
13. });
14. }
15. var cars =["獵豹","捷達","朗逸"];
16. logCars(cars);