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Command Object

A command object is an object which encapsulates the information necessary to invoke a method or function. A command object can:

be scheduled to run later.

be serialized and sent over networks for remote/distributed computation.

help to keep a history of operations.

synchronize data and resolve conflicts.

be cancelled before execution.

be undone after execution.

be grouped to perform atomic operations.

be transformed in various ways such as duplicate removal, joining and splitting for various algorithms. One of the algorithms is Operational Transformation (OT), the base of real-time collaborative software.


RESETRUNFULL
<!DOCTYPE html><html><body><script>

var statusUpdateService = {
   statusUpdates: {},
   sendUpdate: function(status){
      console.log('Status sent: '+status);
       var id = Math.floor(Math.random()*1000000);
       statusUpdateService.statusUpdates[id] = status;
       return id;
   },
   destroyUpdate: function(id){
      console.log('Status removed: '+id);
      delete statusUpdateService.statusUpdates[id];
   }}function createSendStatusCmd(service,status){
   var postId = null;
   var command = function(){
      postId = service.sendUpdate(status);
   }
   command.undo = function(){
      if (postId){
         service.destroyUpdate(postId);
         postId = null;
      }
   }
   command.serialize = function(){
      return {type:'status', action:'post', status:status};
   }
   return command;}// P.T.O.

</script></body><html>
( courtesy of Chapter 4, Node.js Design Patterns by Mario Casciaro)
RESETRUNFULL
<!DOCTYPE html><html><body><script>

// **********************************************function Invoker(){
   this.history = [];}Invoker.prototype.run = function (cmd){
   this.history.push(cmd);
   cmd();
   console.log('Command executed', cmd.serialize());}Invoker.prototype.delay = function(cmd, delay){
   var self = this;
   setTimeout(function(){self.run(cmd);},delay);}Invoker.prototype.undo = function(){
   var cmd = this.history.pop();
   cmd.undo();
   console.log('Command undone', cmd.serialize());}Invoker.prototype.runRemotely = function(cmd){
   var self = this;
   request.post('http://localhost:3000/cmd',
                      {json:cmd.serialize()},
                       function(err){console.log('Command executed remotely',cmd.serialize())});}// **********************************************var invoker = new Invoker();var command = createSendStatusCmd(statusUpdateService,'Hi!');invoker.run(command);invoker.undo();invoker.delay(command,10 * 60 * 60);invoker.runRemotely(command);

</script></body><html>