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include ../../../../_includes/_util-fns
:marked
Everything that we can do in Angular 2 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 2 APIs.
Since TypeScript is a popular language option in Angular 2, 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 2 JavaScript
applications.
<a id="toc"></a>
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## 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)
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**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.**
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a(id="modularity")
.l-main-section
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## 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
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### Importing Angular 2 Code
In TypeScript code, Angular 2 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 2 Code through the ng global
In JavaScript code, when using
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[the Angular 2 packages](../glossary.html#!#scoped-package),
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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 `angular2` in TypeScript:
+makeExample('cb-ts-to-js/js/app/main.js', 'ng2import')(format="." )
tr(style=top)
td
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### Importing and Exporting Application Code
Each file in an Angular 2 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 2 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 2 JavaScript project. In such a project, we would
use CommonJS modules and the `require` function to load Angular 2 framework code.
We would then use `module.exports` and `require` to export and import application
code.
a(id="class-metadata")
.l-main-section
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## Classes and Class Metadata
- var top="vertical-align:top"
table(width="100%")
col(width="50%")
col(width="50%")
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th TypeScript
th ES5 JavaScript
tr(style=top)
td
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### Classes
We put most of our Angular 2 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 2 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 2 classes have one or more TypeScript *decorators*
attached to provide configuration and metadata. For example,
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a component must have a [`@Component`](../api/core/index/Component-decorator.html) decorator.
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+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
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to the [`@Component`](../api/core/index/Component-decorator.html) TypeScript decorator.
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+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 2 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")
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## Input and Output Metadata
- var top="vertical-align:top"
table(width="100%")
col(width="50%")
col(width="50%")
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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),
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we use [`@Input`](../api/core/index/Input-var.html)
and [`@Output`](../api/core/index/Output-var.html) property decorators.
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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 2 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
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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)).
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+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.
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Use the injection support functions `Attribute`, `Host`, `Optional`, `Self`, `SkipSelf` to qualify dependency injection behavior.
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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
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[`@Host`](../api/core/index/Host-var.html) and
[`@SkipSelf`](../api/core/index/SkipSelf-var.html) in the same way -
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by adding `new ng.core.Host()` or `ng.core.SkipSelf()` in the
parameters array.
a(id="other-property-metadata")
.l-main-section
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## Host and Query Metadata
- var top="vertical-align:top"
table(width="100%")
col(width="50%")
col(width="50%")
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th TypeScript
th ES5 JavaScript
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:marked
### Host Decorators
We can use host property decorators to bind a host element to a component or directive.
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The [`@HostBinding`](../api/core/index/HostBinding-var.html) decorator
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binds host element properties to component data properties.
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The [`@HostListener`](../api/core/index/HostListener-var.html) decorator bimds
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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 2 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.
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The [`@ViewChild`](../api/core/index/ViewChild-var.html) and
[`@ViewChildren`](../api/core/index/ViewChildren-var.html) property decorators
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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
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The [`@ContentChild`](../api/core/index/ContentChild-var.html) and
[`@ContentChildren`](../api/core/index/ContentChildren-var.html) property decorators
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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="." )
