Vfrdtyky

Can anybody give me tutorial how this function is working i am not able to understand how this function is working. How this.go function actually working. Any Help would be appreciated. Thanks

var Middleware = function() {};



Middleware.prototype.use = function(fn) {

  var self = this;



  this.go = (function(stack) {

    return function(next) {

      stack.call(self, function() {

        fn.call(self, next.bind(self));

      });

    }.bind(this);

  })(this.go);

};



Middleware.prototype.go = function(next) {

  next();

};

USAGE

var middleware = new Middleware();



middleware.use(function(next) {

  var self = this;

  setTimeout(function() {

    self.hook1 = true;

    console.log('a')

    next();

  }, 10);

});



middleware.use(function(next) {

  var self = this;

  setTimeout(function() {

    self.hook2 = true;

    console.log('b')

    next();

  }, 10);

});



var start = new Date();

middleware.go(function() {

  console.log(this.hook1); // true

  console.log(this.hook2); // true

  console.log(new Date() - start); // around 20

});

The purpose of this code seems to be to build up a sequence of functions, which will then be run one after the other.

The go method's job is to run some code. If you've never called use, then go will run the specified code immediately, with no complications.

The use method lets you insert additional steps to be run. When you call use, the original go method is replaced with a new method. That new method will call the old go method, followed by your custom method. If use is called multiple times, this builds up a sequence of functions. The functions will be called in the order they were passed in to use. The next function starts running when the previous function calls next().

A lot of the complication of the code comes from making sure that the value of this stays what it's expected to be. If that wasn't a requirement, then use could be rewritten like this:

Middleware.prototype.use = function(fn) {

  const oldGo = this.go;

  this.go = next => oldGo(() => fn(next))

}