Functions as Arguments Grammar [REDUX]

Functions as Arguments Grammar [REDUX]
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#1

I’ve been having trouble understanding when to write functions as arguments with brackets and when not to do so and was hoping somebody could clarify it for me.

I feel like I have seen this in other frameworks or libraries but I am working through Redux and it’s what I’ll use as an example.

Sometimes when passing an already defined function to a Redux method, it can be passed just as a constant and others it needs to be followed by brackets. For example:

const store = Redux.createStore(reducerFunction);

That function does not require you to use brackets but:

store.dispatch( actionFunc() );

Does require you to follow it with brackets.
At first, I thought it had to do with ES6 arrow functions but I just passed the challenge below and It would not pass unless I added the brackets to an arrow function without parameters.

[https://learn.freecodecamp.org/front-end-libraries/redux/use-middleware-to-handle-asynchronous-actions/]

So my question is: is there any convention, general or specific for each framework, on how to write functions as arguments?


#2

The first one is a reference to a function: the actual function, not the value it returns. So you are passing a function to a function.

In the second one, you are passing a value, not a function: actionFunc() means execute actionFunc, and from that comes a value.

For example say you had this function that squares a number:

function square(n) {
  return n * n;
}

And you had an array of numbers:

const nums = [2,3,4]

You can do this:

nums.map(square):

Because map takes a function as an argument, then runs it for each element in the array. But you can’t do this:

nums.map( square() )

Because that doesn’t make sense, instead of a function, the value of square if you execute it on its own is undefined, so you would be saying “run undefined in each of the elements in this array”.

You could do

nums.map(n => square(n))

But that is [practically and mathematically] exactly the same as

nums.map(square)

Similarly, these are the same (there may be more arguments, this is just as an example, and always do it like the second example):

const store1 = Redux.createStore(r => reducerFunction(r));
const store2 = Redux.createStore(reducerFunction);

#3

duh! :roll_eyes:

Thank you!, I was over thinking it, I think I’ve read about it and completely forgotten it, wasn’t thinking about the return values or function calling.

Great explanation!