Dart is a new web programming language with libraries, a virtual machine, and tools. Dart helps developers build structured modern web apps. Dart compiles to JavaScript to run across the entire modern web. Dart is inspired by a range of languages such as Smalltalk, Strongtalk, Erlang, C#, and JavaScript.
Dart web language chart sheet
Features of Dart Language:
Object oriented. Everything is an object including primitives and nulls
Optionally typed. You can add type annotations which static checking tools can use to help you find errors in your code, but you don’t have to use them.
Interpreted. Dart is run in a VM, but it is not compiled first. Round-trip time for making changes is very short.
Compatible with JavaScript. You can compile your Dart code to JavaScript and run Dart applications in any modern browser.
FAST! Dart is very fast, much faster than JavaScript in just about every test.
Mixins. Instead of using inheritance, you can use a mixin to add functionality to a class without directly inheriting from another class.
Isolates. Instead of threads, the Dart language uses isolates for concurrency. Isolates can’t actually share any memory, they pass information though messages. It is very hard to shoot yourself in the foot.
Simplified built-in types. Numbers can be either int or double, and you can just use num, if you don’t care. Lists and maps can be declared as literals. An array is just a special case of a list.
Functions are first-class objects. You can pass them around just like any other object. There is even a lambda-like short-hand for creating a one-liner function.
Top level functions and variables. Don’t want to put a function or variable in a class? Good, you don’t have to. In the Dart language, you can declare them anywhere you want.
Simplified classes. There is short-hand for declaring constructors that assign parameters to class members. Class members don’t have protected, private, public. Member variables are automatically properties.
String interpolation. No more string format methods, just use the $variableName in a string to have its value expanded.
Creating your first Dart language App
Step 1:
Go to File –> New Application.
Fill in your application name without space. (for ex: i used “helloworld”)
Leave “Generate sample content” checked.
Select “Web application.”
Step 2:
Open the helloworld.html file and clear out everything in the body element except for the two script tags at the bottom.
The first script tag imports our actual Dart file, just like you would use to add JavaScript to a page.
The second script adds Dart support to the browser.
Step 3:
Add the following HTML to the body tag in the helloworld.html file:
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<button id="theButton" >Click Me</button>
<div id="resultDiv"></div>
This will just create a button and a div. We are going to add some Dart code to respond to a button click and populate the div with some text.
Step 4:
Open the helloworld.dart file and clear out everything in main() and delete the reverseText function.
Notice that there are only two things we really will need in our .dart file. Just an import ‘dart:html’, to import that html library for Dart, and the main function, which executes as soon the DOM content is loaded on the page.
Step 5:
Edit the helloworldweb.dart file to make it look like this:
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import 'dart:html';
void main() {
var button = query("#theButton");
button.onClick.listen(addResult);
}
void addResult(Event e) {
var resultDiv = query("#resultDiv");
resultDiv.text = "You clicked the button";
}
This code simply gets the button using a CSS selector. It uses the query function to do this.
Then we register the addResult function as an event handler for the onClick event for the button.
In the addResult function, we simply query for the resultDiv and change its text.
After you run this example, you should see a result like this:
Step 6:
Now change the Dart code to look like this:
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import 'dart:html';
void main() {
query("#theButton")
.onClick.listen(
(e) => query("#resultDiv").text = "You clicked the button!"
);
}
< content @courtesy oreilly >
Dart is a source code VM
The Dart VM reads and executes source code, which means there is no compile step between edit and run. As with other popular scripting languages, it’s very quick to iterate with Dart. The Dart VM runs on the command line and servers, and can be embedded into browsers. Just point the VM at Dart source code and you’re up and running!
Dart is optionally typed
Dart understands that sometimes you just don’t feel like appeasing a ceremonial type checker. Dart’s inclusion of an optional type system means you can use type annotations when you want, or use dynamic when that’s easier.
For example, you can explore a new idea without having to first think about type hierarchies. Just experiment and use var for your types. Once the idea is tested and you’re comfortable with the design, you can add type annotations.
Here is a comparison between code that uses type annotations, and code that uses var for dynamic. Both of these code snippets have the same runtime semantics:
With type annotations:
Or, without type annotations:
Type annotations are great for the “surface area” of the code (such as method and function signatures), and the tools are getting good enough for you to consider using var inside methods and functions.
Dart supports collection literals
It’s easy to declare lists and maps with Dart. For example, here is a simple list:
And here is a simple map:
Dart is purely object oriented
Dart’s language is clear: everything is an object. It is easy to explain how everything works without having to deal with primitives as a special case. Even calling + on two numbers is modeled as a method call. Numbers, booleans, and even null are all objects.
Dart supports top-level functions and variables
Not everything must live inside of a class. Dart’s libraries can contain top-level functions and variables. You can write whole programs without ever using a class.
Here is a simple Dart library:
Using this library is easy:
Dart’s main function is terse
No more public-static-void-main-String[]-args just to start a program! Dart’s simple top-level main()function is all you need.
Here is an example:
All Dart programs start at the main() function.
Dart lets you put any number of public classes into a file
Organize your project’s files and contents the way you want to. You are not forced to name the file the same as the class, and you aren’t forced to place only one public class in a file. Go ahead, put two classes into one file. Whatever works for you!
Dart has closures and lexically scoped functions
Create functions that can naturally access variables in their enclosing scope, without having to write verbose anonymous inner classes.
Here is an example of a closure in action. The makeAdder function returns a function that closes aroundmakeAdder‘s parameter.
You can use simplify makeAdder by returning an anonymous function:
Dart has mixins
No need to pollute the inheritance hierarchy with utility classes. Use Dart’s mixins to slide in functionality that is clearly not an is-a relationship.
Classes that extend object, don’t have constructors, and don’t call super can be a mixin. Here is an example:
Dart has operator overriding
You can add operators to your class. Here is an example:
Dart has string interpolation
It’s very easy to build a string from variables or expressions. Here is an example of implementing toString()and including the x and y fields in the output.
Dart has noSuchMethod
A class can implement noSuchMethod to handle methods that don’t explicitly exist on the class.
In the following example, the LoggingProxy logs all method calls before they are delegated. The code uses mirrors for run-time reflection and delegation, and noSuchMethod to capture the calls.
You can use the above code like this: