This is the basic skeleton from which all great components originate. The Component decorator is the most important part. Without it, the above example becomes a generic class. Angular relies on decorators to discern a class' schematic type. Component receives metadata as a single object.
Decorators are just JavaScript functions under the hood. They take in arguments as with the metadata object. The metadata object configures a component's basic dependencies. Each fields plays a role. Think of metadata as a big blob of configuration. The decorator takes it so that it can generate the data specific to the component. The decorator decorates the underlying class with data necessary for its class' behavior. A component class that is. The class' signature exports by default so that the component can be imported.
Data drives everything. Components are no exception. Components encapsulate all their data. To receive data externally, a component must explicitly declare it. This form of privacy keeps information from clashing across the component tree.
Data determines what gets displayed from the component class to its template. Components will often initialize a set of members or variables that store data.
They are used throughout the component class logic for convenience. This information fuels the logic resulting in the template and its behavior. See the following example. Note the ways the component interacts with its data.
It first fetches it from.. The data shows up throughout the template. Clicking on the button removes a specific element from allPosts by its index.
You can even change the topmost username by typing into the input box. The above interactions alter the component class' data which in turn updates the component's template HTML. Components provide the backbone logic that facilitates the flow of data. The template HTML makes that data readable to the user. Data often defines the look of an application. Angular connects them through data binding. Think of data binding as a tool for component interaction. The component stores most of its logic and data inside of its class decorated with Component.
This decorator defines the class as a component with template HTML. The template of the component represents the class within the application. The focus here needs to be between the component's class and the template HTML. This is where data binding occurs. Element properties and events get assigned values. These values, defined by the component class, serve either one of two roles. One is to produce data that the template then receives.
The other handles events emitted by the template element. Do not confuse object properties with a DOM element's attributes. Properties and attributes often share the same name and do the same thing. There is one clear distinction however. Remember that attr attributes is a single property of the underlying DOM object.
It maintains the same value after that. Properties each have their own key-value field in a DOM object node. These properties are mutable post-instantiation. Know the difference between attributes and properties. It will lead to a better understanding of how Angular binds data to properties property binding. Exceptions to this are very rare. One last time: Angular binds component data to properties, not attributes! Referring back to the example, the [ … ] in the element's property assignment have special meaning.
Angular reads it and matches its value against component class members. Angular will substitute the value of the matching member attribute. This of course refers to the same component class that hosts the template HTML. The unidirectional flow of data from component to template is complete. The member matched against right assignment of the bracketed property provides the value. Note that changes to the member's value in the component class percolate down to the template.
That is Angular's change detection at work. Changes within the template's scope have no effect on the component class member. This last example implements double curly braces. Angular recognizes these braces and interpolates the matching component class data into the innerHTML of the div. The event pertains to any valid event type. For example, one of the most common event types is click. It emits when you click your mouse. Event handlers are usually member functions of the component class.
The … are special to Angular. Parenthesis tell Angular an event is bounded to the right assignment of handler. The event itself originates from the host element. The handler maps to the identically named handler function of the component class. The unidirectional exchange from the event-bound element to the component class is complete. Emitting events from the handler, while possible, do not impact the template element.
The binding is unidirectional after all. Directives are component elements and attributes created and recognized by Angular. Angular associates the element or attribute with its corresponding class definition. Directive or Component decorates these classes. Both are indicative to Angular that the class performs as a directive. Some directives modify the style of the host element. Other directives display views or insert into existing ones as embedded views. On other words, they alter the HTML layout.
In any case, directives signal the Angular compiler. They mark components for modification depending on the class logic of the directive. Here are three examples of structural directives. Each one has a logical counterpart if , for , and switch. Important note: all three are available through the CommonModule import. If truthy, the element and its innerHTML show up. This is a contrived example. Any member value from the template's component class can be substituted in for true or false.
Microsyntax moves beyond the scope of this article. Know that microsyntax is a short form of logical expression. It occurs as a single string capable of referencing class member values. Arrays are one of the most common iterables. Each array element is assigned the variable potato.
This is all done utilizing microsyntax. That is characteristic of a structural directive. These two structural directives work together to provide switch functionality to template HTML. Notice the [ngSwitch] attribute inside of the div element wrapping the switch.
This chain of structural directives determine which h1 element renders. It passes the value along whereas the switch block determines the final layout of HTML. Remember that stylization and value passing are not the responsibility of structural directives. That concerns attribute directives. Structural directives determine only the layout.
Normally data transforms behind the scenes. With pipes, transforming data can take place in the template HTML. Pipes transform template data directly. Pipes look nice and are convenient. To put it technically, pipes encapsulate data transformation logic. Angular comes prepackaged with a basic set of pipes. Working with a couple of them will develop the intuition to handle the rest. The following list provides three examples. This sections requires a basic understanding of Promises or Observables to fully appreciate.
The AsyncPipe operates on either of the two. In the case of Obervables, AsyncPipe subscribes automatically to the data source. Regardless of where the data comes from, the AsyncPipe subscribes to the source observable. Once the potatoes arrive, either synchronously or asynchronously, the AsyncPipe receives them as an iterable array. The list element then fills up with potatoes. A delete functionality should let users click a delete icon and delete an item. It would also be great to have the option to enter a new item with the return key, instead of clicking the add button.
In this case, we just have one field so we will just get a single value. If we have multiple fields, the submit event will return the values of all the fields in the form.
Here we are?. One more thing. I like to add a little touch of animations. To add animation, import the animations components in your app.
We are done?. You can find the files and code on Github. Angular is easier than you think. Angular is one of the best JavaScript libraries, and it has great support and a nice community. It also has tools that make working with Angular fast and easy, like Angular-cli. Subscribe to this mail-list to learn more about Angular.
If you read this far, tweet to the author to show them you care. Tweet a thanks. Apr 6, May 20, May 22, Update to Angular 6 Jun 29, Oct 10, View code. Demo RealWorld This codebase was created to demonstrate a fully fledged application built with Angular that interacts with an actual backend server including CRUD operations, authentication, routing, pagination, and more. How it works We're currently working on some docs for the codebase explaining where functionality is located, how it works, etc but the codebase should be straightforward to follow as is.
Building the project Run ng build to build the project. Functionality overview The example application is a social blogging site i. About Exemplary real world application built with Angular angular. Releases No releases published.
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