Porting javascript to dart - dart

Question

I'd like to port this javascript code to dart.
function Beagle() {
this.argv_ = null;
this.io = null;
};
Beagle.prototype.run = function() {
this.io = this.argv_.io.push();
};
runCommandClass(Beagle);
the probleme is
How to create object Beagle
How to create prototype object Beagle.prototype.run

Answer 1

This kind of Js code (function definition and prototype changes) can be ported to a Dart class. You can follow these main rules :
function Xxxx(){/* js code to init */} (pseudo Js class) translates to :
class Xxxx {
/// constructor
Xxxx() {
/* Dart code to init */
}
}
when you have contructor parameters like in function Xxxx(param1, param2){/* js code to init */} you have to create an other constructor with those parameters :
class Xxxx {
/// constructor with parameters
Xxxx(param1, param2) {
/* Dart code to init with param1, param2 */
}
}
Xxxx.prototype.method1 = function(p1, p2, p3){/* js code for method */} are like methods that have to be translated to :
class Xxxx {
// .... other code
/// method
method1(p1, p2, p3) {
/* Dart code */
}
}
To make your code more clear you can also add type annotations on methods and constructors. This is recommanded by the Dart Style Guide.
Type annotations are important documentation for how a library should be used. Annotating the parameter and return types of public methods and functions helps users understand what the API expects and what it provides.
For instance :
class Xxxx {
/// constructor
Xxxx(String param1, int param2) {
/* Dart code to init with param1, param2 */
}
/// method
void method1(num p1, String p2, DateTime p3) {
/* Dart code */
}
}

Answer 2

class Beagle { //
Map argv_;
int io;
Map portInfo;
// could make sense to make this a constructor, that depends how the Terminal class uses it (didn't look)
void run(this.argv_) {
this.portInfo_ = JSON.parse(this.argv_['argString']); // not tested
io = argv_['io'].length;
}
void sendString_(String s) { // no idea what the underlines at the end of argv_, sendString_, ... are for
// ...
}
void onRead_(String s) {}
void onTerminalResize_(int width, int height) {}
void exit(code) {
// ...
}
void close() {
// ...
}
}
var b = new Beagle(); // not translated from the JS source - just added to show how to create a new object from the Beagle class
b.run(argvFromSomewhere);
This includes a some guessing about what the intention of the JavaScript code might be.
I prefer using specific types when porting from JavaScript. It helped me a lot finding bugs and understanding the intention. When I guessed the wrong type I get an exception at runtime, then I can reason about why I got an unexpected type and which of my assumptions were wrong.