I have a javascript class, and each method returns a Q promise. I want to know why this is undefined in method2 and method3. Is there a more correct way to write this code?

function MyClass(opts){

  this.options = opts;



  return this.method1()

    .then(this.method2)

    .then(this.method3);

}



MyClass.prototype.method1 = function(){

  // ...q stuff...



  console.log(this.options); // logs opts object



  return deferred.promise;

};



MyClass.prototype.method2 = function(method1resolve){

  // ...q stuff...



  console.log(this); // logs undefined



  return deferred.promise;

};



MyClass.prototype.method3 = function(method2resolve){

  // ...q stuff...



  console.log(this); // logs undefined



  return deferred.promise;

};

I can fix this by using bind:

function MyClass(opts){

  this.options = opts;



  return this.method1()

    .then(this.method2.bind(this))

    .then(this.method3.bind(this));

}

But not entirely sure why bind is necessary; is .then() killing this off?