73 lines
3.0 KiB
Markdown
73 lines
3.0 KiB
Markdown
# JavaScript modules vs. NgModules
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JavaScript and Angular use modules to organize code, and
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though they organize it differently, Angular apps rely on both.
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## JavaScript modules
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In JavaScript, modules are individual files with JavaScript code in them. To make what’s in them available, you write an export statement, usually after the relevant code, like this:
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```typescript
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export class AppComponent { ... }
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```
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Then, when you need that file’s code in another file, you import it like this:
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```typescript
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import { AppComponent } from './app.component';
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```
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JavaScript modules help you namespace, preventing accidental global variables.
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For more information on JavaScript modules, see [JavaScript/ECMAScript modules](https://hacks.mozilla.org/2015/08/es6-in-depth-modules/).
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## NgModules
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<!-- KW-- perMisko: let's discuss. This does not answer the question why it is different. Also, last sentence is confusing.-->
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NgModules are classes decorated with `@NgModule`. The `@NgModule` decorator’s `imports` array tells Angular what other NgModules the current module needs. The modules in the `imports` array are different than JavaScript modules because they are NgModules rather than regular JavaScript modules. Classes with an `@NgModule` decorator are by convention kept in their own files, but what makes them an `NgModule` isn’t being in their own file, like JavaScript modules; it’s the presence of `@NgModule` and its metadata.
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The `AppModule` generated from the [Angular CLI](cli) demonstrates both kinds of modules in action:
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```typescript
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/* These are JavaScript import statements. Angular doesn’t know anything about these. */
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import { BrowserModule } from '@angular/platform-browser';
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import { NgModule } from '@angular/core';
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import { AppComponent } from './app.component';
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/* The @NgModule decorator lets Angular know that this is an NgModule. */
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@NgModule({
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declarations: [
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AppComponent
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],
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imports: [ /* These are NgModule imports. */
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BrowserModule
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],
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providers: [],
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bootstrap: [AppComponent]
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})
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export class AppModule { }
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```
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The NgModule classes differ from JavaScript module in the following key ways:
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* An NgModule bounds [declarable classes](guide/ngmodule-faq#q-declarable) only.
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Declarables are the only classes that matter to the [Angular compiler](guide/ngmodule-faq#q-angular-compiler).
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* Instead of defining all member classes in one giant file as in a JavaScript module,
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you list the module's classes in the `@NgModule.declarations` list.
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* An NgModule can only export the [declarable classes](guide/ngmodule-faq#q-declarable)
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it owns or imports from other modules. It doesn't declare or export any other kind of class.
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* Unlike JavaScript modules, an NgModule can extend the _entire_ application with services
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by adding providers to the `@NgModule.providers` list.
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<hr />
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## More on NgModules
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For more information on NgModules, see:
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* [Bootstrapping](guide/bootstrapping).
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* [Frequently used modules](guide/frequent-ngmodules).
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* [Providers](guide/providers).
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