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Welcome back in the last video we examine the second rule for determining the value of the key word

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this the implicit rule the implicit rule states that when the key word this is inside of a declared

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object its value will always be the closest parent object.

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One thing to note these rules that we are using are not an official part of the JavaScript specification

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so you will not find them there.

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These rules are just a helpful way of keeping track of what the value of the key word this is.

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At the end of the last video we saw an example of when the context of the keyword this changed unexpectedly

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in our Say hello method.

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The first name property became undefined because the keyword this now referred to the dog object.

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So what do we want to explicitly set the value of the keyword this so we can force it to be the person

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object instead of the dog object.

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This is where the third rule comes in.

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Whenever you see the call apply or bind methods you can easily determine what the value of the keyword

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this will be because you get to set it as the first parameter to call apply and bind.

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Before we compare and contrast these three methods.

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One thing to remember is that they can only be used on functions call apply and bind or methods that

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can only be used by functions not by any other data type like strings booleans or objects.

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The first method we're going to talk about is call the first argument to the call method is whatever

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you want the value of the keyword this to be.

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This is commonly called this ARG and can be set to whatever you want.

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The arguments after this ARG are any parameters that you want to pass to the function which you are

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changing the context of the keyword this inside of the sounds confusing but I'll make more sense when

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we see an example.

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And since a function can have an infinite number of arguments we separate each one of them with a comma

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when using call.

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Finally when the call method is used on a function that function is immediately invoked.

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Now let's move on to a plot.

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Apply is almost identical to call except apply only takes two parameters at most the first just like

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call is what we want the value of the key word this to be.

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We call that this ARG.

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The second is an array of arguments that we want to pass to the function in which we are changing the

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value of the keyword this.

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Now let's examine bind.

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Bind is almost identical to call except instead of invoking the function immediately.

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Bind returns a function definition.

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Let's quickly recap what I mean by function definition.

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I'm going to make a function called first function and it is going to return the string hello.

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If I do not invoke the function but examine the variable i created.

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I'm returned a function definition.

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Bind is an extremely powerful function as we can see functions with a different value of the keyword

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this and invoke them at a later point in time.

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Bind is quite valuable when working with asynchronous code like set timeout and is the building block

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for more advanced programming techniques like couriering.

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Let's quickly recap these three methods call apply and bind are used to explicitly said the value of

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the keyword.

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This we use them when we want full control over what the keyword this will refer to.

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So it will have precedence over the first two rules call and apply will immediately invoke the function

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they are called on whereas bind or return a new function definition with the value of the keyword.

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This explicitly set finally call and bind.

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Except an infinite number of parameters whereas apply only takes in two in the next video.

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We'll see an example of call and how we can use it to explicitly set the value of the keyword this.

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See that