When to use take() vs takeUntilDestroyed()?
Summary
TLDRThis video explores the use of RxJS operators 'take' and 'takeUntilDestroyed' with HTTP requests in Angular. It explains how 'take' limits the number of emissions from an observable and is ideal for infinite streams, while 'takeUntilDestroyed' prevents memory leaks by unsubscribing when a component or service is destroyed. The script clarifies that 'take' is unnecessary for one-time HTTP requests like GET, but 'takeUntilDestroyed' can be used to cancel pending requests on navigation. The video includes code examples and a deep dive into Angular and RxJS source code for a comprehensive understanding.
Takeaways
- 😀 The RxJS `take` operator emits a specified number of items from an observable and then automatically completes.
- 🔍 When using `take` with an HTTP request, it doesn't serve a purpose since HTTP requests are inherently one-time operations that complete after emitting a single response.
- 🛠️ The `takeUntilDestroyed` operator is introduced in Angular 16 to automatically complete the observable when a component or service is destroyed, preventing memory leaks.
- 🚫 It's advised against using `takeUntilDestroyed` with HTTP `PUT`, `POST`, or `DELETE` requests because these operations should not be canceled when the user navigates away.
- 🔄 The script demonstrates how the order of operators affects the output, showing that `take` can behave differently depending on its position in the observable pipeline.
- 📚 The source code of Angular and RxJS is explored to understand how HTTP requests are handled and how observables are completed after a response.
- 📈 The `take` operator is useful for limiting the number of emissions from infinite or long-running observables, such as those created by `timer` or `subject`.
- 🔎 The script includes a practical example using a to-do list application to illustrate the effects of the `take` operator on observables.
- ✅ For one-time HTTP `GET` requests, `take` does not change behavior, but `takeUntilDestroyed` can be used to cancel the request if the user navigates away before the response is received.
- 👍 The video encourages viewers to like and subscribe if they find the content useful, highlighting the importance of community engagement for educational content.
Q & A
What is the primary function of the RxJS 'take' operator?
-The 'take' operator emits a specified number of items from an observable and automatically completes after taking the specified number of items. It is useful for limiting the number of emissions from an observable.
How does the 'take' operator interact with other operators in a pipeline?
-The 'take' operator takes the specified number of items from an observable, regardless of whether they pass through filters or not. Once the specified number is reached, the observable completes, even if subsequent items pass through filters.
What is the difference between using 'take' and 'takeUntil' operators with HTTP requests in Angular?
-HTTP requests in Angular are typically one-time operations that complete after emitting a single response. Using 'take(1)' with these requests has no effect since the observable completes after the first emission. 'takeUntilDestroyed' is used to automatically complete the observable when the component or service is destroyed, preventing memory leaks.
Why might 'takeUntilDestroyed' be used with an HTTP GET request?
-While 'takeUntilDestroyed' doesn't prevent the emission of the response in an HTTP GET request, it can be used to cancel the request if the user navigates away before the data is returned, preventing unnecessary processing or subscription handling when the data is eventually returned.
What is the significance of the 'takeUntilDestroyed' operator in Angular applications?
-The 'takeUntilDestroyed' operator is used to automatically unsubscribe from observables when a component or service is destroyed, which helps prevent potential memory leaks and eliminates the need for manual unsubscription.
Why should 'takeUntilDestroyed' not be used with HTTP PUT, POST, or DELETE requests?
-Since HTTP PUT, POST, or DELETE requests are intended to modify data, using 'takeUntilDestroyed' could inadvertently cancel these operations if the user navigates away, which is generally not the desired behavior for modification requests.
How does the 'take' operator handle the order of emissions in an observable sequence?
-The 'take' operator takes the specified number of items from the observable sequence in the order they are emitted, regardless of any filters applied. Once the specified count is reached, the observable completes.
What is the role of the 'filter' operator in the observable pipeline demonstrated in the script?
-The 'filter' operator in the observable pipeline is used to selectively pass items through the pipeline based on a condition. Items that do not meet the condition are not emitted by the pipeline, even if they are taken by the 'take' operator.
What does the script reveal about the internal workings of HTTP requests in Angular?
-The script reveals that Angular's HTTP client sets up an observable for each request, which emits the response and then completes. This behavior means that operators like 'take(1)' do not change the observable's behavior for HTTP requests.
How does the script demonstrate the practical use of RxJS operators in an Angular application?
-The script demonstrates the use of RxJS operators in an Angular application by showing how they can be applied to a to-do list component. It shows how operators like 'take' and 'filter' can be used to control the flow and processing of data in the application.
Outlines
🌐 Understanding HTTP Client Operators: Take vs. TakeUntilDestroyed
This paragraph delves into the comparison between the 'take' and 'takeUntilDestroyed' operators when making HTTP requests using an HTTP client. It begins by examining the 'take' operator, which emits a set number of items from an observable before automatically completing. The paragraph provides a practical example using Angular and RxJS, demonstrating how 'take' can be used to limit the emissions from an observable sequence, such as a to-do list application. The discussion then explores the impact of adding filters and taps to the observable pipeline and how they interact with the 'take' operator. The paragraph concludes with an analysis of using 'take' with HTTP requests, explaining that since HTTP requests are typically one-time operations, the 'take' operator does not significantly alter their behavior.
🔄 The Role of takeUntilDestroyed in Angular
The second paragraph focuses on the 'takeUntilDestroyed' operator introduced in Angular version 16. It discusses how this operator automatically completes the subscription to an observable when its component or service is destroyed, thus preventing memory leaks without requiring manual unsubscription. The source code for 'takeUntilDestroyed' is briefly examined, highlighting its implementation and the creation of a destroy reference. The paragraph also revisits the 'take' operator's source code to illustrate how it tracks emissions and completes the observable once the specified count is reached. The discussion concludes with guidance on when to use 'take' versus 'takeUntilDestroyed'. It suggests using 'take' for limiting emissions from unlimited observables like timers or subjects, and 'takeUntilDestroyed' for unsubscribing from long-running operations to prevent memory leaks. Additionally, it advises against using 'takeUntilDestroyed' with HTTP put, post, or delete requests, as it may cancel the operation unintentionally when the user navigates away.
Mindmap
Keywords
💡HTTP Client
💡RxJS
💡Observable
💡Take Operator
💡TakeUntilDestroyed Operator
💡Unsubscribe
💡Memory Leak
💡Filter Operator
💡Component
💡Service
Highlights
The RxJS 'take' operator is used to emit a specified number of items from an observable and then automatically completes.
The 'take' operator is ideal for limiting the number of emissions from an unlimited observable, such as one created by a timer or subject.
In a sample application, the 'take' operator is demonstrated to emit only two numbers before completing the observable.
Adding complexity with a 'filter' before 'take' and a 'tap' after 'take' shows the operator's behavior in a pipeline with additional operators.
The 'take' operator takes the specified number of items and completes the observable, regardless of whether they pass through a 'filter'.
Using 'take' with an HTTP request is unnecessary because HTTP requests are inherently one and done, emitting a single response before completing.
The source code of Angular's HTTP client reveals that observables complete after emitting the response from an HTTP request.
The 'takeUntilDestroyed' operator was introduced in Angular version 16 to prevent memory leaks by automatically unsubscribing when a component or service is destroyed.
The 'takeUntilDestroyed' operator is useful for long-running operations but should not be used with HTTP put, post, or delete requests.
The source code of 'takeUntilDestroyed' shows how it sets up a destroy handler to complete the observable when the component or service is destroyed.
The 'take' operator's source code is examined to understand how it tracks emissions and completes the observable after a certain count.
For HTTP GET operations, 'take' is unnecessary, but 'takeUntilDestroyed' can be used to cancel the operation if the user navigates away.
It's recommended not to use 'takeUntilDestroyed' with HTTP PUT, POST, or DELETE operations because users typically expect these modifications to be completed even after navigation.
The video concludes with a summary of when to use 'take' and 'takeUntilDestroyed', emphasizing their roles in managing observable emissions and preventing memory leaks.
Transcripts
hey I was recently asked if it would be
better to use take or take until
destroyed when issuing an HTTP request
with HTTP client in this video we
examine the take operator and evaluate
its use with HTTP operations we crack
open the angular and rxj source code
then we compare the take and takeen till
destroyed operators for use in H HTTP
requests let's take a look the rxjs take
operator emits a specified number of
items from an observable it
automatically completes after taking the
specified number of items it's great for
limiting unlimited observables I'm in
stack Blitz here is a sample application
that I've built in Prior videos the link
to this code is in this video's notes in
the to-do list component I'll add some
code to demonstrate the take operator
here we create an observable that emits
a set of numbers but you can imagine in
a real application this would be an
observable emitting from a timer or
subject what will we see in the
counil yep we see the take operator
emits two and three and then completes
the observable the remaining numbers
aren't emitted let's add some complexity
I'll in insert a filter above the take
and a tap after the take and let's turn
the oneline arrow function in the filter
operator into a multi-line arrow
function I'll add curly braces and a
return statement then add some logging
within the filter so we know the filter
is being
executed now what will we see in the CSO
the observable emits two which passes
through the filter and is taken by the
take operator and emitted from the
pipeline the observable emits three the
three is processed by the filter
operator but does not pass through the
filter and is not taken or emitted then
the observable emits four which passes
through the filter is taken and emitted
from the pipeline so this take emits two
and four and completes the
observable now let's move the filter to
the end of the
pipeline what will we see scrolling the
console window the pipeline only emits
two is that what you expected the
observable emits two which is
taken it passes through the filter
operator and is emitted from the
pipeline the observable emits three
which is taken it's processed by the
filter operator but does not pass
through the filter and and is not
emitted from the pipeline but the take
operator has now taken two items and
completes the observable even though
only one of the items was emitted from
the pipeline so the take takes the
specified number of items and completes
the
observable I'll comment this out but
leave it here in the sample code for you
to try out now what about using take
with an HTTP request let's look at the
to-do service I'll remove the take till
destroyed and let's uncomment the
logging so we can see the emitted value
scrolling the console and drilling down
we see the data then get is complete
what would adding a take one here do
nothing basically all HTTP requests are
one and done that means that the
response is emitted and the observable
completes no need for a take one same is
true with other HTTP requests such as
put post or delete these HTTP requests
are one and done so take one doesn't do
anything I'll remove this code to
confirm that the HTTP requests indeed
complete after they emit let's take a
quick look at the source code I'm in the
angular GitHub repository HTTP SRC
folder looking at the xhr dots file here
is the code that executes our HTTP
requests scrolling down to the return
statement we see that the code sets up a
new observable we aren't going to go
through all of this code but if we
scroll down to if okay online 209 we see
that if the request returns a successful
response the code calls observable nextt
to emit that response then on line 222
the code calls the observable complete
method thereby completing the observable
so after an HTTP request receives a
response that response is emitted and
the observable is
completed what about take until
destroyed let's jump over to the source
code for that the take until destroyed
operator was introduced in angular
version 16 it automatically complet fets
unsubscribing from the observable when
its component or service is destroyed
this prevents potential memory leaks and
doesn't require a manual
unsubscribe I covered this useful
operator in detail in my prior video
used taken till destroyed to unsubscribe
from angulars
observables and then walk through why we
should not use taken till destroyed when
issuing put post or delete requests in
this prior video
don't use take till destroyed with
angular's HTTP put post or delete
looking at line 23 we see the
implementation of Taken till destroyed
it creates a destroy ref if one isn't
provided it sets up an UND destroy
Handler looking at line 35 it then uses
the rxjs taken till operator to
automatically complete when the
component or service is destroyed let's
also take a quick look at the source
code for the take operator it's in the
rxjs repository the take operator Starts
Here on line
47 this code keeps track of the number
of emissions it has seen if the number
is less than the count passed into the
operator it calls next to emit the value
and when that c number equals the count
it calls next to emit that value and
calls complete to to complete the
observable going back to the code so
when should we use take versus take
until destroyed use take with unlimited
observables such as timer or subject to
limit the number of emissions the take
will complete the observable when the
specified number of emissions are taken
use take until till destroyed to
unsubscribe from long running operations
such as a timer or a subject
this completes the observable since take
till destroyed executes when the
component or service is destroyed it
prevents potential memory leaks I
demonstrated that in my prior taken till
destroyed video since an HTTP get
operation is one and done we don't need
to worry about memory leaks and using
take doesn't do anything however
consider using taken till destroyed to
cancel the get operation when the user
navigates away before the data is
returned using taken till destroyed
completes the observable which prevents
any pipeline operators or the Subscribe
Handler from executing when the data is
later returned same with the HTTP put
post or delete operations using take
doesn't do anything but unlike retrieve
operations the user most likely does not
want to cancel their modification when
navigating away so don't use take till
destroyed with these
operations thanks for watching and if
this content was useful please like And
subscribe
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