The purpose of this style guide is to provide guidance on building Angular applications by showing the conventions we use and, more importantly, why we choose them.
We apply the [Single Responsibility Principle](https:\/\/en.wikipedia.org/wiki/Single_responsibility_principle) to all Components, Services, and other symbols we create. This helps make our app cleaner, easier to read and maintain, and more testable.
**Why?** One component per file makes it far easier to read, maintain, and avoid collisions with teams in source control.
**Why?** One component per file avoids hidden bugs that often arise when combining components in a file where they may share variables, create unwanted closures, or unwanted coupling with dependencies.
**Why?** Small functions help avoid hidden bugs that come with large functions that share variables with external scope, create unwanted closures, or unwanted coupling with dependencies.
Naming conventions are hugely important to maintainbility and readability. This guide will recommend naming conventions for the file name and the symbol name.
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### General Naming Guidelines
<a id="02-01"></a>
#### Style 02-01
- Use consistent names for all symbols following a pattern that describes the symbol's feature then its type. The recommended pattern is `feature.type.ts`.
**Why?** Naming conventions help provide a consistent way to find content at a glance. Consistency within the project is vital. Consistency with a team is important. Consistency across a company provides tremendous efficiency.
**Why?** The naming conventions should simply help we find our code faster and make it easier to understand.
**Why?** Names of folders and files should clearly convey their intent. For example, `app/heroes/hero-list.component.ts` may contain a component that manages a list of heroes.
- Use dashes to separate words. Use dots to separate the descriptive name from the type.
- Use consistent names for all components following a pattern that describes the component's feature then its type. A recommended pattern is `feature.type.ts`.
- Use conventional suffixes for the types including `*.service.ts`, `*.component.ts`, `*.pipe.ts`. Invent other suffixes where desired for our team, but take care in having too many.
- Use consistent names for all services named after their feature. Use UpperCamelCase for services. Suffix services with `Service` when it is not clear what they are (e.g. when they are nouns).
**Why?** Provides a consistent way to quickly identify and reference services.
**Why?** Clear service names such as `logger` do not require a suffix.
**Why?** Service names such as `Credit` are nouns and require a suffix and should be named with a suffix when it is not obvious if it is a service or something else.
- Use lowerCamelCase for naming the selectors of our directives.
**Why?**: Keeps the names of the properties defined in the directives that are bound to the view consistent with the attribute names.
**Why?**: The Angular 2 HTML parser is case sensitive and will recognize lowerCamelCase
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### Custom Prefix for Components
<a id="02-07"></a>
#### Style 02-07
- Use a custom prefix for the selector of our components. For example, the prefix `toh` represents from **T**our **o**f **H**eroes and the prefix `admin` represents an admin feature area.
- Use a prefix that identifies the feature area in the app.
- In small apps, use a prefix that identifies the app.
**Why?**: Prevents name collisions
**Why?**: Our Components and elements are easily identified
**Why?**: Makes it easier to promoted and share our feature in other apps.
```
/* avoid */
// HeroComponent is in the Tour of Heroes feature
@Component({
selector: 'hero'
})
export class HeroComponent {}
// UsersComponent is in an Admin feature
@Component({
selector: 'users'
})
export class UsersComponent {}
```
```
/* recommended */
// HeroComponent is in the Tour of Heroes feature
@Component({
selector: 'toh-hero'
})
export class HeroComponent {}
// UsersComponent is in an Admin feature
@Component({
selector: 'admin-users'
})
export class UsersComponent {}
```
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### Custom Prefix for Directives
<a id="02-08"></a>
#### Style 02-08
- Use a custom prefix for the selector of our directives (for instance below is used the prefix `toh` from **T**our **o**f **H**eroes).
All of the app's code goes in a root folder named `app`. All content is 1 feature per file. Each component, service, pipe is in its own file. All 3rd party vendor scripts are stored in another root folder and not in the `app` folder. We didn't write them and we don't want them cluttering our app. Use the naming conventions for file in this guide.
- Structure the app such that we can `L`ocate our code quickly, `I`dentify the code at a glance, keep the `F`lattest structure we can, and `T`ry to stay DRY. The structure should follow these 4 basic guidelines, listed in order of importance.
*Why LIFT?*: Provides a consistent structure that scales well, is modular, and makes it easier to increase developer efficiency by finding code quickly. Another way to check our app structure is to ask ourselves: How quickly can we open and work in all of the related files for a feature?
**Why?** We find this to be super important for a project. If our team cannot find the files we need to work on quickly, we will not be able to work as efficiently as possible, and the structure needs to change. We may not know the file name or where its related files are, so putting them in the most intuitive locations and near each other saves a ton of time. A descriptive folder structure can help with this.
**Why?** We spend less time hunting and pecking for code, and become more efficient. If this means we want longer file names, then so be it. Be descriptive with file names and keeping the contents of the file to exactly 1 component. Avoid files with multiple components, multiple services, or a mixture.
There are deviations of the 1 per file rule when we have a set of very small features that are all related to each other, as they are still easily identifiable.
**Why?** Nobody wants to search 7 levels of folders to find a file. In a folder structure there is no hard and fast number rule, but when a folder has 7-10 files, that may be time to create subfolders. We base it on our comfort level. Use a flatter structure until there is an obvious value (to help the rest of LIFT) in creating a new folder.
**Why?** Being DRY is important, but not crucial if it sacrifices the others in LIFT, which is why we call it T-DRY. We don’t want to type `hero-view.component.html` for a view because, well, it’s obviously a view. If it is not obvious or by convention, then we name it.
- Create folders named for the feature they represent. When a folder grows to contain more than 7 files, start to consider creating a folder for them. our threshold may be different, so adjust as needed.
**Why?** A developer can locate the code, identify what each file represents at a glance, the structure is flat as can be, and there is no repetitive nor redundant names.
**Why?** The LIFT guidelines are all covered.
**Why?** Helps reduce the app from becoming cluttered through organizing the content and keeping them aligned with the LIFT guidelines.
**Why?**: Components have templates containing HTML and optional Angular template syntax. They are most associated with putting content on a page, and thus are more closely aligned with elements.
**Why?**: Components are derived from Directives, and thus their selectors can be elements, attributes, or other selectors. Defining the selector as an element provides consistency for components that represent content with a template.
- Use [`@Input`](https://angular.io/docs/ts/latest/api/core/Input-var.html) and [`@Output`](https://angular.io/docs/ts/latest/api/core/Output-var.html) instead of the `inputs` and `outputs` properties of the [`@Directive`](https://angular.io/docs/ts/latest/api/core/Directive-decorator.html) and [`@Component`](https://angular.io/docs/ts/latest/api/core/Component-decorator.html) decorators:
**Why?**: If we ever need to rename the name of the property, or event name associated to [`@Input`](https://angular.io/docs/ts/latest/api/core/Input-var.html) or respectively [`@Output`](https://angular.io/docs/ts/latest/api/core/Output-var.html) we can modify it on a single place.
**Why?**: The metadata declaration attached to the directive is shorter and thus more readable.
**Why?**: Placing the decorator on the same line makes for shorter code and still easily identifies the property as an input or output.
- Avoid renaming inputs and outputs, when possible.
**Why?**: May lead to confusion when the output or the input properties of a given directive are named a given way but exported differently as a public API.
**Why?** Placing members in a consistent sequence makes it easy to read and helps we instantly identify which members of the component serve which purpose.
**Why?**: This is consistent with built-in events such as button clicks.
**Why?**: Angular allows for an [alternative syntax](https://angular.io/docs/ts/latest/guide/template-syntax.html#!#binding-syntax) `on-*`. If the event itself was prefixed with `on` this would result in an `on-onEvent` binding expression.
**Why?**: The name of the property, or method name associated to @HostBinding or respectively @HostListener should be modified only in a single place - in the directive's controller. In contrast if we use host we need to modify both the property declaration inside the controller, and the metadata associated to the directive.
- Services should have a single responsibility that is encapsulated by its context. Once a service begins to exceed that singular purpose, a new one should be created.
**Why?:** When a service has multiple responsibilities, it becomes difficult to test.
**Why?:** When a service has multiple responsibilities, every Component or Service that injects it now carries the weight of them all.
**Why?** When providing the service to a top level component, that instance is shared and available to all child components of that top level component.
**Why?** This is not ideal when two different components need different instances of a service. In this scenario it would be better to provide the service at the component level that needs the new and separate instance.
- Use the `@Injectable` class decorator instead of the `@Inject` parameter decorator when we are using types as tokens for the dependencies of a service.
**Why?**: The Angular DI mechanism resolves all the dependencies of our services based on their types declared with the services' constructors.
**Why?**: When a service accepts only dependencies associated with type tokens, the `@Injectable()` syntax is much less verbose compared to using `@Inject()` on each individual constructor parameter.
- Refactor logic for making data operations and interacting with data to a service. Make data services responsible for XHR calls, local storage, stashing in memory, or any other data operations.
**Why?** The component's responsibility is for the presentation and gathering of information for the view. It should not care how it gets the data, just that it knows who to ask for it. Separating the data services moves the logic on how to get it to the data service, and lets the component be simpler and more focused on the view.
**Why?** This makes it easier to test (mock or real) the data calls when testing a component that uses a data service.
**Why?** Data service implementation may have very specific code to handle the data repository. This may include headers, how to talk to the data, or other services such as `Http`. Separating the logic into a data service encapsulates this logic in a single place hiding the implementation from the outside consumers (perhaps a component), also making it easier to change the implementation.
Client-side routing is important for creating a navigation flow between a component tree hierarchy, and composing components that are made of many other child components.
Use file templates or snippets to help follow consistent styles and patterns. Here are templates and/or snippets for some of the web development editors and IDEs.
### Visual Studio Code
- [Visual Studio Code](https://code.visualstudio.com/) snippets that follow these styles and guidelines.
