When to use take() vs takeUntilDestroyed()?

Summary

This 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

00:00

🌐 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.

05:02

🔄 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.

Keywords

💡HTTP Client

An HTTP Client is a software component that makes requests to HTTP servers. In the context of the video, it refers to the mechanism used to perform HTTP operations, such as GET, POST, PUT, or DELETE requests. The video discusses how to handle these requests using RxJS operators, emphasizing the importance of understanding how HTTP clients work with observables.

💡RxJS

RxJS is a library for reactive programming using Observables, which makes it easier to compose asynchronous or callback-based code. The video uses RxJS to demonstrate how to handle HTTP requests and control the emission of values from observables. RxJS operators like 'take' and 'takeUntilDestroyed' are discussed to show how they can be used in different scenarios with HTTP requests.

💡Observable

In RxJS, an Observable is a core concept that represents a collection of future values or events. The video explains how observables are used to handle data emissions from HTTP requests. It shows how the 'take' operator can limit the number of values emitted by an observable, which is crucial for managing data flow and preventing memory leaks.

💡Take Operator

The 'take' operator in RxJS is used to emit a specified number of items from an observable and then automatically complete. The video provides examples of how the 'take' operator can be used to limit the number of emissions from an observable, such as a timer or a subject, and discusses its use with HTTP requests, noting that it doesn't affect one-time HTTP operations like GET.

💡TakeUntilDestroyed Operator

The 'takeUntilDestroyed' operator is a utility in Angular that automatically completes the subscription to an observable when a component or service is destroyed. This helps prevent memory leaks by ensuring that subscriptions are cleaned up appropriately. The video explains the implementation of this operator and cautions against its use with HTTP PUT, POST, or DELETE requests.

💡Unsubscribe

Unsubscribing is the process of tearing down a subscription to an observable to prevent memory leaks and stop the execution of further operators or handlers. The video discusses the importance of unsubscribe operations, especially in the context of 'takeUntilDestroyed', which automatically handles this process when a component or service is destroyed.

💡Memory Leak

A memory leak occurs when a computer program incorrectly manages memory allocation, leading to increased memory usage that can cause performance issues or system crashes. The video highlights the importance of preventing memory leaks in web applications by properly managing subscriptions to observables, especially in long-running operations.

💡Filter Operator

The 'filter' operator in RxJS is used to pass only certain values through an observable based on a condition. The video demonstrates how the 'filter' operator can be used in conjunction with the 'take' operator to control the flow of data. It shows an example where a filter is applied before and after the 'take' operator, affecting which values are emitted.

💡Component

In the context of Angular, a component is a fundamental building block used to create user interfaces. The video mentions components in relation to the 'takeUntilDestroyed' operator, which is designed to automatically unsubscribe from observables when an Angular component is destroyed, thus preventing potential memory leaks.

💡Service

A service in Angular is a class that can be injected into components to provide specific functionality or data. The video discusses how services can also benefit from the 'takeUntilDestroyed' operator to ensure that subscriptions to observables are properly cleaned up when the service is no longer needed, preventing memory leaks.

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