Object Oriented JavaScript Tutorial #7 - Method Chaining

alright then so now we've got the basics of how to create classes add on these properties and these different methods right here I want to introduce you to a little trick called method chaining but what does that really mean exactly well right down here where we're calling these different methods we're saying user one login or user to log out right and then if we wanting to call another method for example on user one after this we'd have to go to the next line and say user one dot log out this time okay now instead of what if we wanted to do something like this so get rid of that and then say login dot or log out so we perform one method then we chain on another method when this is done this is called method chaining right here now right now if we did this it's not going to work I can demo that I'll press save and we'll get an error right here it says cannot read property log out of undefined now what that means essentially is that we're trying to call this on undefined so when we call this user 1 dot login we're getting returned undefined yeah we're calling this function and it's logging this to the console but the return value of this is undefined so how do we kind of combat this well to demo this first of all I want to create a new method and this method is going to be called update school so let's create this method first of all update school and inside here what I want to do is update the score or add one to the score of this user so say for example whatever a new user signs up whenever we create a new user this way we'll give them a score property so I'll say this to school and then initially we'll set that to zero to begin with so new users all have a score of zero to begin with we don't pass it in as a parameter right it's the same for every user ok so whenever we call update score on a user what I want to do is take their current score and then increase it by one so what I'll do is say this dot score plus plus right then what I'll do is log something to the console I'll say console dot log and this email so the court uses email and comet and I'll say score is now and then comet after this and then I'll output this score so the current uses school alright so it should be something like a Ryu at ninjas calm score is now five or six depending on what the score is so let's just try this what I'll do is save it and then over in the console I'll say user one update school first of all so now we can see that it's one if I call it again and it should be two if I call it again it should be three because we're increasing the score property by one each time but if I do use it to don't orbit eight school then this should just start out at one then two etc okay so they've both got their own score property which is updating and whatever we call this method now the whole idea of this lesson was method chaining so how then do we do this we don't want to return an undefined value whenever we call a method what we want to do is return the instance of that object now we know that the instance of the object is stored in this right here so all we need to do is say okay well once you've done this then return this so now every time we call this method update score on a user now what we're doing is doing all of this functionality right here and then we're returning this which is that instance of the object that particular user so if we're returning that particular user we can then just do another method on that user right so we can chain them now or we should be able to at least so let's return this for each individual method right here return this like so and then let's give this a whirl down here what I'm gonna do is say user want to update score and I'm gonna call update score again so it does it twice then I'll say logout and in fact to begin with what we'll do is say login all right so all of these different methods were chaining together now now we couldn't do this before but now that were returning the object every time we call one of these methods we should be able to chain these methods because if you think about it we're calling the method and then it's returning this which is essentially just user 1 back here so we're saying user 1 update school then we're returning this again so this value is now user 1 so we're saying user 1 2 updates go again and so forth that's the whole idea behind method chaining so I've saved that let's see if this works okay so first of all right ninjas comm just logged in score is now 1 scores now to just logged out awesome so now that is all working and that my friends is how we do method chaining