observable | Simple script to listen and dispatch events
kandi X-RAY | observable Summary
kandi X-RAY | observable Summary
Observable is a generic tool to send and receive events. It's a common pattern to isolate modules without forming a dependency or "coupling". By using events a large program can be broken into smaller and simpler units. Modules can be added, removed, or modified without affecting the other parts of the application. A common practice is to split the application into a single core and multiple extensions. The core sends events any time something remarkable happens: a new item is being added, an existing item is being removed, or something is loaded from the server. By using the observable the extensions can listen to these events and react to them. They extend the core so that the core is not aware of these modules. This is called "loose coupling". These extensions can be custom tags (UI components) or non-UI modules. Once the core and events are carefully designed the team members are enabled to develop the system on their own without disturbing others.
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- Bind an event listener
observable Key Features
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Community Discussions
Trending Discussions on observable
QUESTION
I was playing around with some API concepts and noticed something peculiar in Rust's Iterator trait.
I have the following trait definition:
...ANSWER
Answered 2022-Apr-11 at 00:51A similar question was asked over on the Rust forum. To summarize, the full signature for Iterator::for_each
is
QUESTION
Take these examples :
...ANSWER
Answered 2022-Mar-25 at 18:37The question is probably more towards how Structural Directive works rather than the Async Pipe. as
and let
syntax are part of Angular Template syntax that Structural Directive makes use of.
There is no difference from the Angular Template syntax side of things. They are valid syntax of Angular template.
However, they're different in how they would be strongly typed. Take a look at the following code of ng_if.ts
from Angular source
QUESTION
Apparently throwError(error)
is now deprecated. The IntelliSense of VS Code suggests throwError(() => new Error('error')
. new Error(...)
accepts only strings. What's the correct way to replace it without breaking my HttpErrorHandlerService
?
ANSWER
Answered 2021-Aug-04 at 19:08Instead of this:
QUESTION
I'm new to angular. I've been trying to sort columns but I keep on getting this error:
Argument of type 'Event' is not assignable to parameter of type 'SortEvent'. Type 'Event' is missing the following properties from type 'SortEvent': column, direction - ngtsc(2345).
Any suggestions on how to make this work?
s-product-management.component.html:
...ANSWER
Answered 2021-Aug-21 at 14:06$event
is not the same type as SortEvent, as you need. $event will always contain a lot of key-value pairs, unless you are using with anything other than legacy elements.
QUESTION
The standard defines several 'happens before' relations that extend the good old 'sequenced before' over multiple threads:
[intro.races]
11 An evaluation A simply happens before an evaluation B if either
(11.1) — A is sequenced before B, or
(11.2) — A synchronizes with B, or
(11.3) — A simply happens before X and X simply happens before B.[Note 10: In the absence of consume operations, the happens before and simply happens before relations are identical. — end note]
12 An evaluation A strongly happens before an evaluation D if, either
(12.1) — A is sequenced before D, or
(12.2) — A synchronizes with D, and both A and D are sequentially consistent atomic operations ([atomics.order]), or
(12.3) — there are evaluations B and C such that A is sequenced before B, B simply happens before C, and C is sequenced before D, or
(12.4) — there is an evaluation B such that A strongly happens before B, and B strongly happens before D.[Note 11: Informally, if A strongly happens before B, then A appears to be evaluated before B in all contexts. Strongly happens before excludes consume operations. — end note]
(bold mine)
The difference between the two seems very subtle. 'Strongly happens before' is never true for matching pairs or release-acquire operations (unless both are seq-cst), but it still respects release-acquire syncronization in a way, since operations sequenced before a release 'strongly happen before' the operations sequenced after the matching acquire.
Why does this difference matter?
'Strongly happens before' was introduced in C++20, and pre-C++20, 'simply happens before' used to be called 'strongly happens before'. Why was it introduced?
[atomics.order]/4
says that the total order of all seq-cst operations is consistent with 'strongly happens before'.
Does it mean that it's not consistent with 'simply happens before'? If so, why not?
I'm ignoring the plain 'happens before', because it differs from 'simply happens before' only in its handling of memory_order_consume
, the use of which is temporarily discouraged, since apparently most (all?) major compilers treat it as memory_order_acquire
.
I've already seen this Q&A, but it doesn't explain why 'strongly happens before' exists, and doesn't fully address what it means (it just states that it doesn't respect release-acquire syncronization, which isn't completely the case).
Found the proposal that introduced 'simply happens before'.
I don't fully understand it, but it explains following:
- 'Strongly happens before' is a weakened version of 'simply happens before'.
- The difference is only observable when seq-cst is mixed with aqc-rel on the same variable (I think, it means when an acquire load reads a value from a seq-cst store, or when an seq-cst load reads a value from a release store). But the exact effects of mixing the two are still unclear to me.
ANSWER
Answered 2022-Jan-02 at 18:21Here's my current understanding, which could be incomplete or incorrect. A verification would be appreciated.
C++20 renamed strongly happens before
to simply happens before
, and introduced a new, more relaxed definition for strongly happens before
, which imposes less ordering.
Simply happens before
is used to reason about the presence of data races in your code. (Actually that would be the plain 'happens before', but the two are equivalent in absence of consume operations, the use of which is discouraged by the standard, since most (all?) major compilers treat them as acquires.)
The weaker strongly happens before
is used to reason about the global order of seq-cst operations.
This change was introduced in proposal P0668R5: Revising the C++ memory model, which is based on the paper Repairing Sequential Consistency in C/C++11 by Lahav et al (which I didn't fully read).
The proposal explains why the change was made. Long story short, the way most compilers implement atomics on Power and ARM architectures turned out to be non-conformant in rare edge cases, and fixing the compilers had a performance cost, so they fixed the standard instead.
The change only affects you if you mix seq-cst operations with acquire-release operations on the same atomic variable (i.e. if an acquire operation reads a value from a seq-cst store, or a seq-cst operation reads a value from a release store).
If you don't mix operations in this manner, then you're not affected (i.e. can treat simply happens before
and strongly happens before
as equivalent).
The gist of the change is that the synchronization between a seq-cst operation and the corresponding acquire/release operation no longer affects the position of this specific seq-cst operation in the global seq-cst order, but the synchronization itself is still there.
This makes the seq-cst order for such seq-cst operations very moot, see below.
The proposal presents following example, and I'll try to explain my understanding of it:
QUESTION
Imagine a service ABService
with a method isAResponsible: () => boolean
and two modules: AModule
and BModule
.
The question is: Is it possible to switch between AModule
and BModule
depending on what isAResponsible
returns? And how do we 'reroute' and rerender if the value of isAResponsible
changes? ABService
may have several dependencies to other services so it would be preferable to make use of the DI system somehow.
Example:
If the route of interest is /aorb
and ABService.isAResponsible
returns true
, than we would like to route AModule
. If ABService.isAResponsible
returns false
however we want BModule
to manage further routing. Note that everything should happen on a shared route.
I tried it with guards and canActivate
/canLoad
but didn't succeed:
ANSWER
Answered 2021-Dec-17 at 16:50You can you try this instead, I have just checked locally it works, just think it in a different way and you have your solution :)
QUESTION
I have an API call that may return some data or may return something falsey if no data exists. If there is data, I want to tap
out of the stream and do some side effects, but if falsey, I want no side effects to happen but still display my template code.
I am using an async pipe to get that data in the template, but if the data is falsey, it will not display.
I have seen the technique to wrap the ngIf
with an object so it evaluates to truthy, but it doesn't seem the correct solution for my code.
My template:
...ANSWER
Answered 2021-Dec-16 at 08:28You can always try to keep it as semantic as possible. Your approach using map
is not a bad idea, it's just that you actually lose the access to your data. It's probably better to split it up in two Observables
:
QUESTION
I have an angularfire authentication service which works absolutely fine - except it wont refresh the token.
My refresh code:
...ANSWER
Answered 2021-Nov-30 at 14:21Firebase handle the token refresh process, so there is no need to manually refresh the token. Firebase auth state can be read from 'authState' property.
QUESTION
Note: I think I was able to to reproduce this (see stackblitz example). The error there is printed in the console as "
INTERNAL ASSERTION FAILED: Expected a class definition
". This is different to what I get locally but to me this looks like the same issue.Anyway, just comment out line 15 in
app.component.ts
and the error will disappear.
I am trying to get started with Firebase but when I install & compile the Angular project I am getting the following error:
Module not found: Error: Package path ./compat is not exported from package /home/sfalk/workspaces/web-mobile/node_modules/firebase (see exports field in /home/sfalk/workspaces/web-mobile/node_modules/firebase/package.json)
The interesting thing is that I am only getting this error when I am injecting my AuthService
e.g. like this:
ANSWER
Answered 2021-Dec-02 at 15:09You need to change your import from:
QUESTION
I am managing my state in Angular app by using Behavior Subject. I am using two services. One to perform send and get request using web sockets and one to store the data in an observable. As soon as the data is retrieved I pass the data to the behavior subject. I am having an issue here. Everything is working perfectly except, when I delete the item and press the back button. Some of my data gets lost during this process. I don't know why is this happening. Here's my code:
...cart.store.ts // for managing state
ANSWER
Answered 2021-Nov-01 at 10:41The problem is in the deleteCart
function. You subscribe to the observable but never unsubscribe. So every time you call next()
, The deleteCart
runs again and deletes an item.
You can use BehaviorSubject.value
to get the current items. The result should see like this:
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