Is it necessary to include both `import 'rxjs/Rx'` and `import { Observable } from '@rxjs/Observable'` in my code?

Question

Is it necessary to include both `import 'rxjs/Rx'` and `import { Observable } from '@rxjs/Observable'` in my code?

import { Injectable } from '@angular/core';
import { Headers, Http, Response } from '@angular/http';
import { Observable } from '@rxjs/Observable';
import 'rxjs/Rx';
import 'rxjs/add/observable/throw';
@Component({});
export shellModule{}

I found this code snippet in my Angular application that I borrowed from another source. The exported module definitions have been removed for simplicity. I am utilizing it to create a service for API calls.

One thing that puzzles me is why the Observable object is imported separately even though the entire rxjs library has already been imported. If an entire module is being imported, why import specific objects individually? I posed this question on the original forum where I came across this code, but unfortunately, there was no response. I am curious to know if there are any benefits or optimizations related to importing individual objects over entire modules.

javascript angular typescript

Answer 1

Answer №1

Generally speaking:

In the realm of Typescript, handling modules involves either importing the entire library using import * as rx from 'rxjs/Rx', or selecting a specific exported module within the library for usage in order for the compiler to load in the types.

Focusing on importing only the necessary modules allows for utilizing tree shaking through Angular's AOT compilation. While this optimization is not directly performed by the typescript compiler, it can be achieved with the assistance of a tool like rollup. Although helpful in optimizing code later on, it does not occur automatically.

In terms of compilation efficiency, importing the entire library may cause some minor slowdown in the compiler's processing speed... although this drawback is more pronounced with extremely intricate libraries.

Personally, I find importing specific modules preferable as it results in cleaner calling code, eliminating the need for global names to access specific ones. For instance, comparing rx.Observable to Observable. This distinction is particularly evident when working with libraries such as lodash (although rxjs presents a higher level of complexity).

Importing entire libraries as shown in your example line: import 'rxjs/Rx' seems illogical to me. It is advisable to import only specific exported modules. Consider removing it, observing any resulting errors, and then opting for the * as rx syntax instead.

Regarding rxjs specifically – obtaining particular operators can be slightly tricky, as demonstrated in this question. The method to acquire specific operators involves using:

import 'rxjs/add/observable/from'

- which also necessitates adjustments to your webpack configuration as outlined in the answer provided in the referenced question.

Answer 2

Generally speaking:

In the realm of Typescript, handling modules involves either importing the entire library using import * as rx from 'rxjs/Rx', or selecting a specific exported module within the library for usage in order for the compiler to load in the types.

Focusing on importing only the necessary modules allows for utilizing tree shaking through Angular's AOT compilation. While this optimization is not directly performed by the typescript compiler, it can be achieved with the assistance of a tool like rollup. Although helpful in optimizing code later on, it does not occur automatically.

In terms of compilation efficiency, importing the entire library may cause some minor slowdown in the compiler's processing speed... although this drawback is more pronounced with extremely intricate libraries.

Personally, I find importing specific modules preferable as it results in cleaner calling code, eliminating the need for global names to access specific ones. For instance, comparing rx.Observable to Observable. This distinction is particularly evident when working with libraries such as lodash (although rxjs presents a higher level of complexity).

Importing entire libraries as shown in your example line: import 'rxjs/Rx' seems illogical to me. It is advisable to import only specific exported modules. Consider removing it, observing any resulting errors, and then opting for the * as rx syntax instead.

Regarding rxjs specifically – obtaining particular operators can be slightly tricky, as demonstrated in this question. The method to acquire specific operators involves using:

import 'rxjs/add/observable/from'

- which also necessitates adjustments to your webpack configuration as outlined in the answer provided in the referenced question.

Answer 3

Answer №2

Exploring the modules exported by rxjs/Rx:

export { Subject, AnonymousSubject } from './Subject';
export { Observable } from './Observable';
export { Operator } from './Operator';
export { Observer } from './Observer';
export { Subscription } from './Subscription';
export { Subscriber } from './Subscriber';
export { AsyncSubject } from './AsyncSubject';
export { ReplaySubject } from './ReplaySubject';
export { BehaviorSubject } from './BehaviorSubject';
...

import './add/observable/bindCallback';
import './add/observable/bindNodeCallback';
import './add/observable/combineLatest';
...

The module exports various RxJs classes and imports operators from the add directory. This means that the entire library is being loaded. However, it does not export any global object directly. To use the exported classes, you must utilize named exports like so:

import * as Rx from 'rxjs/Rx'

This method allows you to access an exported class such as:

Rx.Observable.of(12, 3);

If you prefer a setup similar to loading the library via a bundle with a global Rx object, you would need to import Observable separately:

import { Observable } from '@rxjs/Observable';
Observable.of(1);

It is discouraged to import both together, but may be done if you wish to avoid importing every operator individually.

For further guidance on correctly importing operators from the rxjs package, refer to this resource.

Answer 4

Exploring the modules exported by rxjs/Rx:

export { Subject, AnonymousSubject } from './Subject';
export { Observable } from './Observable';
export { Operator } from './Operator';
export { Observer } from './Observer';
export { Subscription } from './Subscription';
export { Subscriber } from './Subscriber';
export { AsyncSubject } from './AsyncSubject';
export { ReplaySubject } from './ReplaySubject';
export { BehaviorSubject } from './BehaviorSubject';
...

import './add/observable/bindCallback';
import './add/observable/bindNodeCallback';
import './add/observable/combineLatest';
...

The module exports various RxJs classes and imports operators from the add directory. This means that the entire library is being loaded. However, it does not export any global object directly. To use the exported classes, you must utilize named exports like so:

import * as Rx from 'rxjs/Rx'

This method allows you to access an exported class such as:

Rx.Observable.of(12, 3);

If you prefer a setup similar to loading the library via a bundle with a global Rx object, you would need to import Observable separately:

import { Observable } from '@rxjs/Observable';
Observable.of(1);

It is discouraged to import both together, but may be done if you wish to avoid importing every operator individually.

For further guidance on correctly importing operators from the rxjs package, refer to this resource.

Is it necessary to include both `import 'rxjs/Rx'` and `import { Observable } from '@rxjs/Observable'` in my code?

Answer №1

Answer №2

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