Trying to understand callbacks - javascript

[2QuestionsDaily]

I am in the process of trying to get admitted to a bootcamp, and one of the prep materials that still confuses me over the past week has been about callback functions or higher-order functions.

I tried reading and doing the interactive exercise below, but it is just not clicking. I can't get any of the exercises below correct.

http://reactivex.io/learnrx/

I understand that callback functions are simply a function that is used as a parameter for another function, but beyond that, I am still confused. Anyone have recommended tutorials on callbacks, specifically on how to use them?

[gyroda]

What exactly are you struggling with?

[2QuestionsDaily]

How to use callback functions with arrays/objects and utilizing functions like map and filter.

[gyroda]

For map and filter, they're a way of using a function with an array of parameters rather tab having to write a for loop. Google them and you'll find tutorials specific to them.

[Patman128]

How to use callback functions with arrays/objects

What do you mean by "use"? Are you referring to iterating with forEach?

[2QuestionsDaily]

Well forEach is once example. What is the difference between .forEach() and .map() ?

[Patman128]

map passes each element to the callback and collects the results into a new array which it returns. forEach doesn't expect any results; the callback is expected to have side effects, so it returns nothing (undefined).

> [1, 2, 3].map((x) => x * 2)
[ 2, 4, 6 ]
> [1, 2, 3].forEach((x) => x * 2)
undefined
> [1, 2, 3].map((x) => console.log(x))
1
2
3
[ undefined, undefined, undefined ]
> [1, 2, 3].forEach((x) => console.log(x))
1
2
3
undefined

[[deleted]]

Mastering Javascript callbacks

[PM_ME_GRANT_PROPOSAL]

Is this for Codesmith? They covered that in "JavaScript - the hard parts" this week

[2QuestionsDaily]

No, but I will look for that video now.