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JavaScript JavaScript and the DOM (Retiring) Responding to User Interaction Functions as Parameters

My understanding of Passing say() function????

I would like to clarify my understanding is correct for this step. The block of code is written on multiple lines so it can be mind boggling at first.

  1. We are calling exec() and passing it 2 arguments.
  2. The first argument is a function named say(something)
  3. The second argument is the string we would like to pass into say(something)
  4. The arguments then get executed as a function

In otherwords we are passing a function into a function as the first argument, and the second "arg" as a string.

The main function here is....

exec(func, arg);

The first argument for exec() is a function

function say(something) {
   console.log(something);
},

The second argument for exec() is where it gets a bit tricky for me. It's a string that gets passed into say(something) ????

'Hi, there' 

Which function of the two is 'Hi, there' being being passed to?

  1. exec(func, arg)
  2. say(something?

2 Answers

Dane Parchment
MOD
Dane Parchment
Treehouse Moderator 10,727 Points

I believe it is being passed into both!

If you remember correctly JavaScript treats functions like first class citizens (in functional programming this is referred to as a high-order function), this means that functions can be used just like any other data type within JavaScript!

In this case the function exec(func, args); is simply executing a function with the provided arguments. So if we follow the trail of the exec function then we will see that this is how it works:

exec(func, args); will probably look like this if we were to fully write it out:

function exec(func, args) {
func(args);
}

This shows us that if we were to use the other function say(); as the func parameter and Hi, there for the args parameter, then we know that these two parameters are first being used by exec.

Then exec calls the func parameter as a function and places the args parameter within func as a parameter for that function.

So in order of execution:

  1. Exec is called
  2. Exec takes in both parameters: exec(say, 'Hi there');
  3. Exec calls the say function and places 'Hi there' within it as the function dictates: func(args) == say('Hi there')
  4. say will then `console.log('Hi there')
  5. Exec has completed it's task!

It's much easier to understand when you break it down like this. Thanks for the explanation.