angular-cn/public/docs/js/latest/cookbook/ts-to-js.jade

include ../../../../_includes/_util-fns

:marked
  Everything that we can do in Angular in TypeScript, we can also do
  in JavaScript. Translating from one language to the other is mostly a
  matter of changing the way we organize our code and the way we access
  Angular APIs.

  Since TypeScript is a popular language option in Angular, many of the
  code examples you see on the Internet as well as on this site are written
  in TypeScript. This cookbook contains recipes for translating these kinds of
  code examples to ES5, so that they can be applied to Angular JavaScript
  applications.

<a id="toc"></a>
:marked
  ## Table of contents

  [Modularity: imports and exports](#modularity)

  [Classes and Class Metadata](#class-metadata)
  
  [Input and Output Metadata](#property-metadata)
  
  [Dependency Injection](#dependency-injection)
  
  [Host and Query Metadata](#other-property-metadata)

  **Run and compare the live <live-example name="cb-ts-to-js">TypeScript</live-example> and <live-example name="cb-ts-to-js" lang="js">JavaScript</live-example>
  code shown in this cookbook.**

a(id="modularity")
.l-main-section
:marked
  ## Importing and Exporting

- var top="vertical-align:top"
table(width="100%")
  col(width="50%")
  col(width="50%")
  tr
    th TypeScript
    th ES5 JavaScript
  tr(style=top)
    td
      :marked
        ### Importing Angular Code

        In TypeScript code, Angular classes, functions, and other members
        are imported with TypeScript `import` statements:

      +makeExample('cb-ts-to-js/ts/app/main.ts', 'ng2import')(format="." )

    td
      :marked
        ### Accessing Angular Code through the ng global

        In JavaScript code, when using
        [the Angular packages](../glossary.html#!#scoped-package),
        we can access Angular code through the global `ng` object. In the
        nested members of this object we'll find everything we would import
        from `@angular` in TypeScript:

      +makeExample('cb-ts-to-js/js/app/main.js', 'ng2import')(format="." )

  tr(style=top)
    td
      :marked
        ### Importing and Exporting Application Code

        Each file in an Angular TypeScript application constitutes a
        TypeScript module. When we want to make something from a module available
        to other modules, we `export` it.

      +makeExample('cb-ts-to-js/ts/app/hero.component.ts', 'appexport')(format="." )

      :marked
        In other modules we can then `import` things that have been exported
        elsewhere.

      +makeExample('cb-ts-to-js/ts/app/main.ts', 'appimport')(format="." )

    td
      :marked
        ### Sharing Application Code

        In an Angular JavaScript application, we load each file to the page
        using a `<script>` tag. Each file can make things available to other
        files via the shared global `window` scope.

        We often introduce an application namespace
        object (such as `"app"`) onto `window` and attach everything we need
        to share to that namespace object. 
        We also wrap our code in an 
        [Immediately Invoked Function Expression (IIFE)](https://en.wikipedia.org/wiki/Immediately-invoked_function_expression).
        These practices together prevent our code from
        polluting the global scope.

      +makeExample('cb-ts-to-js/js/app/hero.component.js', 'appexport')(format="." )

      :marked
        We can then access anything from this shared namespace in
        other files.

      +makeExample('cb-ts-to-js/js/app/main.js', 'appimport')(format="." )

      :marked
        Note that the order of `<script>` tags on the page is significant. 
        We must load a file that defines a shared member before
        a file that uses that member.

.alert.is-helpful
  :marked
    Alternatively, we can use a module loader such as Webpack or
    Browserify in an Angular JavaScript project. In such a project, we would
    use CommonJS modules and the `require` function to load Angular framework code.
    We would then use `module.exports` and `require` to export and import application
    code.


a(id="class-metadata")
.l-main-section
:marked
  ## Classes and Class Metadata

- var top="vertical-align:top"
table(width="100%")
  col(width="50%")
  col(width="50%") 
  tr
    th TypeScript
    th ES5 JavaScript
  tr(style=top)
    td
      :marked
        ### Classes

        We put most of our Angular TypeScript code into TypeScript classes.

      +makeExample('cb-ts-to-js/ts/app/hero.component.ts', 'class')(format="." )

    td
      :marked
        ### Constructors and Prototypes

        ES5 JavaScript has no classes. We use the constructor
        pattern instead which works with Angular as well as classes do.

      +makeExample('cb-ts-to-js/js/app/hero.component.js', 'constructorproto')(format="." )

  tr(style=top)
    td
      :marked
        ### Metadata with Decorators

        Most Angular classes have one or more TypeScript *decorators*
        attached to provide configuration and metadata. For example,
        a component must have a [`@Component`](../api/core/index/Component-decorator.html) decorator.

      +makeExample('cb-ts-to-js/ts/app/hero.component.ts', 'metadata')(format="." )

    td
      :marked
        ### Metadata with the Annotations Array

        In JavaScript, we can attach an `annotations` array to a constructor
        to provide metadata. 
        Each item in the array corresponds to a TypeScript decorator.

        In the following example, we create a new instance of `Component` that corresponds
        to the [`@Component`](../api/core/index/Component-decorator.html) TypeScript decorator.

      +makeExample('cb-ts-to-js/js/app/hero.component.js', 'metadata')(format="." )

      :marked
        ### Metadata with The Class Convenience API

        The pattern of creating a constructor and decorating it with metadata
        is so common that Angular provides an alternative convenience API for it.
        This API lets us define everything in a single expression.

        With this API we first call the `ng.core.Component` function,
        followed by a chained `Class` method call. The argument to `Class`
        is an object that defines the constructor and the instance methods
        of the component:

      +makeExample('cb-ts-to-js/js/app/hero-dsl.component.js', 'component')(format="." )

      :marked
        Similar APIs are also available for other decorators. You can define a
        directive:
        
      code-example.
        var MyDirective = ng.core.Directive({
          ...
        }).Class({
          ...
        });
      
      :marked
        Or a pipe:
        
      code-example.
        var MyPipe = ng.core.Pipe({
          name: 'myPipe'
        }).Class({
          ...
        });

  tr(style=top)
    td
      :marked
        ### Interfaces

        When defining classes that need to implement a certain method, it
        is common to use TypeScript interfaces that enforce that the 
        method signature is correct. Component lifecycle methods like `ngOnInit`
        are one example of this pattern. `ngOnInit` is defined in the `OnInit`
        interface.

      +makeExample('cb-ts-to-js/ts/app/hero-lifecycle.component.ts')(format="." )

    td
      :marked
        ### Implementing Methods without Interfaces

        TypeScript interfaces are purely for developer convenience
        and are not used by Angular at runtime. This means that in JavaScript
        code we don't need to substitute anything for interfaces. We can just
        implement the methods.

      +makeExample('cb-ts-to-js/js/app/hero-lifecycle.component.js')(format="." )

a(id="property-metadata")
.l-main-section
:marked
  ## Input and Output Metadata

- var top="vertical-align:top"
table(width="100%")
  col(width="50%")
  col(width="50%") 
  tr
    th TypeScript
    th ES5 JavaScript
  tr(style=top)
    td
      :marked
        ### Input and Output Decorators

        In TypeScript, property decorators are often used to provide additional metadata
        for components and directives.

        For [inputs and outputs](../guide/template-syntax.html#inputs-outputs), 
        we use [`@Input`](../api/core/index/Input-var.html)
        and [`@Output`](../api/core/index/Output-var.html) property decorators.
        They may optionally specify input and output binding names if we want them to be
        different from the class property names.

      +makeExample('cb-ts-to-js/ts/app/hero-io.component.ts')(format="." )

      .alert.is-helpful
        :marked
          In TypeScript we can also use the `inputs` and `outputs` array metadata 
          instead of the `@Input` and `@Output` property decorators.
    td
      :marked
        ### Inputs and Outputs in Component Metadata

        There is no equivalent of a property decorator in ES5 JavaScript. Instead, 
        we add comparable information to the `Component` (or `Directive`) metadata.
        
        In this example, we add `inputs` and `outputs` array attributes
        containing the input and output property names. 
        If we need a binding name that is different from the
        property itself, we use the `propertyName: bindingName` syntax.

      +makeExample('cb-ts-to-js/js/app/hero-io.component.js')(format="." )


.l-main-section
:marked
  ## Dependency Injection

- var top="vertical-align:top"
table(width="100%")
  col(width="50%")
  col(width="50%") 
  tr
    th TypeScript
    th ES5 JavaScript
  tr(style=top)
    td
      :marked
        ### Injection by Type

        Angular can often use TypeScript type information to
        determine what needs to be injected.

      +makeExample('cb-ts-to-js/ts/app/hero-di.component.ts')(format="." )

    td
      :marked
        ### Injection with Parameter Tokens

        Since no type information is available in ES5 JavaScript,
        we must identify "injectables" in some other way.

        We attach a `parameters` array to the constructor function. 
        Each array item is the dependency injection token that identifies the thing to be injected. 
        Often the token is the constructor function for the class-like dependency.

      +makeExample('cb-ts-to-js/js/app/hero-di.component.js')(format="." )

      :marked
        When using the class convenience API, we can also supply the parameter
        tokens by wrapping the constructor in an array.

      +makeExample('cb-ts-to-js/js/app/hero-di-inline.component.js')(format="." )

  tr(style=top)
    td
      :marked
        ### Injection with the @Inject decorator

        When the thing being injected doesn't correspond directly to a type,
        we use the `@Inject()` decorator to supply the injection token.
        
        In this example, we're injecting a string identified by the "heroName" token.

      +makeExample('cb-ts-to-js/ts/app/hero-di-inject.component.ts')(format="." )

    td
      :marked
        ### Injection with plain string tokens

        In JavaScript we add the token string to the injection parameters array.

      +makeExample('cb-ts-to-js/js/app/hero-di-inject.component.js','parameters')(format="." )
      
      :marked
        Alternatively, we can create a token with the `Inject` method and
        add that to the constructor array in the annotations like this:
        
      +makeExample('cb-ts-to-js/js/app/hero-di-inject.component.js','ctor')(format="." )        

  tr(style=top)
    td
      :marked
        ### Additional Injection Decorators

        We can attach additional decorators to constructor parameters
        to qualify the injection behavior. We can mark
        optional dependencies with the [`@Optional`](../api/core/index/Optional-var.html),
        inject host element attributes with [`@Attribute`](../api/core/index/Attribute-var.html),
        inject content child queries with [`@Query`](../api/core/index/Query-var.html)
        and inject view child queries with [`@ViewQuery`](../api/core/index/ViewQuery-var.html)).

      +makeExample('cb-ts-to-js/ts/app/hero-di-inject-additional.component.ts')(format="." )

    td
      :marked
        ### Additional Injection Metadata with Nested Arrays 

        To achieve the same effect in JavaScript, use the constructor array notation
        in which the injection information precedes the constructor function itself.
        
        Use the injection support functions `Attribute`, `Host`, `Optional`, `Self`, `SkipSelf` to qualify dependency injection behavior.
        
        Use a nested array to combine injection functions.

      +makeExample('cb-ts-to-js/js/app/hero-di-inject-additional.component.js')(format="." )

      :marked
        We can apply other additional parameter decorators such as
        [`@Host`](../api/core/index/Host-var.html) and
        [`@SkipSelf`](../api/core/index/SkipSelf-var.html) in the same way -
        by adding `new ng.core.Host()` or `ng.core.SkipSelf()` in the
        parameters array.


a(id="other-property-metadata")
.l-main-section
:marked
  ## Host and Query Metadata

- var top="vertical-align:top"
table(width="100%")
  col(width="50%")
  col(width="50%") 
  tr
    th TypeScript
    th ES5 JavaScript  
  tr(style=top)
  
    td
      :marked
        ### Host Decorators

        We can use host property decorators to bind a host element to a component or directive.
        The [`@HostBinding`](../api/core/index/HostBinding-var.html) decorator
        binds host element properties to component data properties. 
        The [`@HostListener`](../api/core/index/HostListener-var.html) decorator bimds
        host element events to component event handlers.
        
      +makeExample('cb-ts-to-js/ts/app/heroes-bindings.component.ts')(format="." )
      
      .alert.is-helpful
        :marked
          In TypeScript we can also use `host` metadata 
          instead of the `@HostBinding` and `@HostListener` property decorators.
    td
      :marked
        ### Host Metadata
        
        We add a `host` attribute to the component metadata to achieve the
        same effect as `@HostBinding` and `@HostListener`. 
        
        The  `host` value is an object whose properties are host property and listener bindings:
        
        * Each key follows regular Angular binding syntax: `[property]` for host bindings
          or `(event)` for host listeners.
        * Each value identifies the corresponding component property or method.
        
      +makeExample('cb-ts-to-js/js/app/heroes-bindings.component.js')(format="." )

  tr(style=top)
    td
      :marked
        ### Query Decorators
        
        There are several property decorators for querying the descendants of
        a component or directive.
        
        The [`@ViewChild`](../api/core/index/ViewChild-var.html) and
        [`@ViewChildren`](../api/core/index/ViewChildren-var.html) property decorators
        allow a component to query instances of other components that are used in
        its view.
        
      +makeExample('cb-ts-to-js/ts/app/heroes-queries.component.ts', 'view')(format="." )

      :marked
        The [`@ContentChild`](../api/core/index/ContentChild-var.html) and
        [`@ContentChildren`](../api/core/index/ContentChildren-var.html) property decorators
        allow a component to query instances of other components that have been projected
        into its view from elsewhere.
        
      +makeExample('cb-ts-to-js/ts/app/heroes-queries.component.ts', 'content')(format="." )
      
      .alert.is-helpful
        :marked
          In TypeScript we can also use the `queries` metadata 
          instead of the `@ViewChild` and `@ContentChild` property decorators.      
    td
      :marked
        ### Query Metadata
        
        We access a component's view children by adding a `queries` attribute to
        the component metadata. It should be an object where:
        
        * Each key is the name of a component property that will hold the view children
        * Each value is an instance of either `ViewChild` or `ViewChildren`.
        
      +makeExample('cb-ts-to-js/js/app/heroes-queries.component.js', 'view')(format="." )

      :marked
        We add *content* child queries to the same `queries` attribute
        in the same manner, using instances of `ContentChild` or `ContentChildren`:
        
      +makeExample('cb-ts-to-js/js/app/heroes-queries.component.js', 'content')(format="." )