Angular Articles

Angular 2 Property and Event Bindings

Have you noticed that many of the directives built-in to AngularJS are missing in Angular 2.0? Well there two reasons for that; “property bindings” and “event bindings”. The various binding types in Angular 2 remove the need for many of the directives built into the prior version of the framework.
Here are a few examples of Angular 2.0 property bindings:
Usage
AngularJS Directive
Angular 2 Property Binding
Hide/unhide an element
ng-hide = “expression”
[hidden]=”expression”
Disable an element (ie Button)
ng-disabled = “expression”
[disabled]=”expression”
Set href for an anchor tag
ng-href = “expression”
[href]=”expression”
Set src for an image tag
ng-src = “expression”
[src]= “expression”
Here “expression” can take a number of forms:
Example Expression
Refers to:
“myVariable”
A component property named myVariable
“true”,
“2 + 2”,
“myVar * 3”,
“http://{{url}}”
An expression that will be evaluated by Angular
“getValue()”,
“myMethod()”
A call to a method in the component
In addition to property bindings Angular 2 includes event binding syntax which also replaces various AngularJS directives. Here are some examples:
Usage
AngularJS Directive
Angular 2 Property Binding
Bind code to a click event
ng-click = “expression”
(click) = “expression”
Bind code to input keyup event
ng-keyup = “expression”
(keyup) = “expression”
Bind code to mouseover event
ng-mouseover = “expression”
(mouseover) = “expression”
Bind code to submit event
ng-submit = “expression”
(submit) = “expression”
Here an “expression” is typically either an angular expression or a component method call.
The addition of property and event binding syntax in Angular 2 opens up binding to all DOM properties and events and dramatically reduces the number of built-in directives the Angular development team needs to maintain.
For more information on property binding see:
For more information on event binding see:

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Angular 2 Programming Languages

Programming Languages for Angular Development

Angular 2 differs from Angular JS in regards to programming language support. With Angular JS you generally program in JavaScript. With Angular 2 the official site provides example code in several languages; JavaScript, TypeScript and Dart.

JavaScript is an implementation of the ECMAScript standard. Several versions exist including ES5 and ES6. Most current browsers fully support JavaScript ES5. This means that code compliant with ES5 will run on most most browsers without modification. ES6 on the other hand may not be supported and is typically converted to ES5 before it gets to the browser. The more recent version of JavaScript (ES6) adds features and makes certain tasks easier. It is not clear when browsers will be fully ES6 compliant.

TypeScript and Dart are language super sets of JavaScript. This means they include all the features of JavaScript but add many helpful features as well. But just like the ES6 version of JavaScript they don’t work on current browsers. To work around this limitation there are utilities to convert code written in their non-browser-compliant syntax back to JavaScript ES5. In this way they provide the developer with advanced features and still allow code to be run on existing browsers. The process of converting code from one language to another is referred to as ‘transpilation’. Technically this conversion is performed by a language pre-processor that, although it does not compile anything, is commonly referred to as a compiler.

TypeScript is an open source language that is developed and maintained by Microsoft. It provides type safety, advanced object oriented features, and simplified module loading. Angular 2 itself is built using TypeScript. The documentation support is better on the Angular 2 site for TypeScript than it is for the other options. So although you could write your Angular 2 apps in pure ES5 JavaScript you may find it more difficult and find less support if you get into trouble than if you bite the bullet and spends some time learning TypeScript.

Dart is another alternative for programming Angular 2 applications. It is similar in features to TypeScript and has its own loyal following. If your team is already versed in Dart and is looking to start developing in Angular 2 it could be a good choice. That being said,  in the rest of this post, we will be concentrating on TypeScript.

Code Example

A basic Angular 2 component coded in TypeScript:

import { Component } from '@angular/core';
@Component({
selector: 'hello-app',
template: '<h1>Hello Angular 2</h1>'
})
export class AppComponent { }

 

The same component coded in JavaScript ES5:

(function(app) {
app.AppComponent = ng.core.Component({
selector: 'hello-app',
template: '<h1>Hello Angular 2</h1>'
})
.Class({
constructor: function() {}
});
})(window.app || (window.app = {}));

 As you can see the TypeScript version is more concise and easy to read.

 

TypeScript Usage Basics

TypeScript support is provided by the Node.js ‘typescript’ package. To use typescript you first need to load Node.js and the Node Package Manager (npm). Once Node.js is installed on you system you would use the following command to install TypeScript support:

npm install -g typescript

This will install the TypeScript compiler and allow you to run it from the command line using the following command:

tsc

There are generally three methods to execute tsc. The first method involves passing the name of the TypeScript code file you want compiled on the command line:

tsc filename.ts

Here’s a simple TypeScript code file:

// app.ts
var msg:string = "Hello Typescript!";
function getMessage(message: string){
return message;
}
console.log(getMessage(msg));

Compiling this file produces a JavaScript file with the same name as the TypeScript file but with an extension of “.js”.

tsc app.ts
(produces app.js)

You can test the file by running it using Node.js like this:

node app.js

As your application gets more complex and you have multiple *.ts files in one or more directories you may want to take advantage of the second method of running tsc. To do this you will first need to set up a tsconfig.json config file. Among other things this file tells tsc which directories contain the files you wish to compile. After placing this file in the root of your project tsc will compile any *.ts files it finds whenever they are modified and saved. To use this method you launch tsc in a terminal window and then edit your *.ts files in any text editor. As you save your files they will automatically be converted to JavaScript.

The third method involves using a text editor plugin to determine when you have saved a *.ts file. When that happens the editor itself will call tsc to perform the conversion. This kind of plugin is available for the Atom text editor. Microsoft Visual Studio also includes this type of support. For those who don’t want to load the complete Visual Studio development system Microsoft’s Visual Studio Core text editor also includes TypeScript support.

Conclusion

Using TypeScript significantly simplifies the code you need to write when creating Angular 2 applications. Although TypeScript can’t be executed by browsers directly there are several ways to convert TypeScript into code that browsers can work with.

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