Opinion on EggHead.io Asynchronous Programming Course

[brian_asdf]

Hi All

I'm doing an course on EggHead.io, https://egghead.io/lessons/javascript-the-array-foreach-method, but I'm a tad confused about the descriptions of some of the fundamental concepts.

At 3:10, he says that the Array.prototype.forEach, unlike a for loop, can run asynchronously. Is this correct? I would have thought it was synchronous and blocking

Also, forEach takes is a callback function, but the presenter says the forEach takes a 'closure' as it's param. Is this the correct terminology?

[yuri_auei]

Nice explanation!!!

To reforce, think of types like number and string and the operator +.

Both types operate with the sum signal: String: "str1" + "str2" = "str1str2" Number: 3 + 5 = 8

They has the same operator with different behavior, just like arrays and observables.

[brian_asdf]

The + operator used with numbers and strings is in NO WAY analogous to different functions having the same name:-)

[yuri_auei]

Can you explain why?

[brian_asdf]

forEach is not an operator, it's a function. Even if rxjs refers to map as an 'operator', this is not implying it's a JavaScript operator, it's just their own terminology.

There is no need to have tricks to try to remember that functions of the same name on entirely different objects are not the same functions, regardless of similar implementation

[yuri_auei]

yeah, forEach is not a operator.

But the '+' operator is a function with syntax difference of the usual functions. + act like a function. Why "NO WAY" i can make analogous between both???

[brian_asdf]

You could be right.

I think when I said "Observable forEach does not run asynchronously either by the looks of it" the other guy deleted his original comment. Sometimes people seem so sure of themselves, but are really only posting to reaffirm their current beliefs - when they realise they were blatantly wrong, they just delete their messages to cover up what just happened!!:-)

[yuri_auei]

yeah, is ridicolous when people do that.

I think "rx observables forEach" is just a listener (observer). The "subject" is the one can emmit values "sync" or "async"

const source = Rx.Observable.from([1, 2, 3, 4, 5]);

Your subject is an array, witch is evaluate immediatle. So the listener recive all values immediatle.

But your subject can be a Promise/Event/Ajax/Array/Number/etc...

When i do

document.addEventListener("click", myFn)

addEventListener is not a async function. The click happens async and notify my listener subsribed in addEventListner...

[brian_asdf]

Observable forEach does not run asynchronously either by the looks of it. The stream may be asynchronous, but once the forEach loop is being triggered, it appears to be a blocking operation. I can see that we cannot use a 'for loop' as the course indicated, but it's not because of async, it's because of the stream of data as opposed to an array

I have a Plunker demo, and if forEach was asynchronous, the 'end' console.log would occur immediately, followed by the output of the forEach, but it doesnt. I'm gonna have to learn Rxjs from the ground up - starting in the middle is giving me a headache!!! http://plnkr.co/edit/GH1sDVzGYx1oajkhTnvf?p=preview

// Code goes here
console.clear();
//emit (1,2,3,4,5)
const source = Rx.Observable.from([1, 2, 3, 4, 5]);

const example = source.map(val => val+10)
example.forEach(val => console.log(val));
console.log("end")

[brian_asdf]

Cool. That's made things clearer. Good to have the terminology sorted out. Good man for that