为什么dart生成的javascript文件如此庞大？

Question

I have the following dart code:

$ cat helloworld.dart
main() => print('Hello world!');
$ 

The javascript code generated by the dart compiler for the above code is as follows:

$ cat helloworld.dart.app.js 
function native_ListFactory__new(typeToken, length) {
  return RTT.setTypeInfo(
      new Array(length),
      Array.$lookupRTT(RTT.getTypeInfo(typeToken).typeArgs));
}
function native_ListImplementation__indexOperator(index) {
  return this[index];
}
function native_ListImplementation__indexAssignOperator(index, value) {
  this[index] = value;
}
function native_ListImplementation_get$length() {
  return this.length;
}
function native_ListImplementation__setLength(length) {
  this.length = length;
}
function native_ListImplementation__add(element) {
  this.push(element);
}
function native_BoolImplementation_EQ(other) {
  return typeof other == 'boolean' && this == other;
}
function native_BoolImplementation_toString() {
  return this.toString();
}

<snapped>

var static$uninitialized = {};
var static$initializing = {};
function $inherits(child, parent) {
  if (child.prototype.__proto__) {
    child.prototype.__proto__ = parent.prototype;
  } else {
    function tmp() {};
    tmp.prototype = parent.prototype;
    child.prototype = new tmp();
    child.prototype.constructor = child;
  }
}
isolate$inits.push(function(){
  isolate$current.Duration$DartMILLISECONDS_PER_MINUTE$field = static$uninitialized;
  isolate$current.Duration$DartMILLISECONDS_PER_HOUR$field = static$uninitialized;
  isolate$current.Duration$DartMILLISECONDS_PER_DAY$field = static$uninitialized;
  isolate$current.Duration$DartSECONDS_PER_HOUR$field = static$uninitialized;
  isolate$current.Duration$DartSECONDS_PER_DAY$field = static$uninitialized;
  isolate$current.Duration$DartMINUTES_PER_DAY$field = static$uninitialized;
}
);
RunEntry(unnamedd9297f$main$member, this.arguments ? (this.arguments.slice ? [].concat(this.arguments.slice()) : this.arguments) : []);
$

And the size of helloworld.dart.app.js is 102k!

When ran in optimize mode, it generated the following javascript - helloworld.dart.js which is of size 20k

$ cat helloworld.dart.js 
var e;function f(a,b){if(b>=0&&b<a.length)return b;h(i(b))};var j={},k={};function aa(a,b,c){if(b)a.g=function(){return b.call(c)}}function ba(a,b,c,d){function g(b,g,t,m){return a.call(c,d,b,g,t,m)}aa(g,b,c);return g}function l(a,b){if(a.prototype.__proto__)a.prototype.__proto__=b.prototype;else{var c=function(){};c.prototype=b.prototype;a.prototype=new c;a.prototype.constructor=a}}function ca(a,b){return typeof a=="number"&&typeof b=="number"?a+b:a.na(b)}function da(a){a/=4;return a<0?Math.ceil(a):Math.floor(a)}
function o(a,b){if(a===void 0)return b===void 0;else if(typeof a==typeof b&&typeof a!="object")return a===b;return a.G(b)}function h(a){a&&typeof a=="object"&&Error.captureStackTrace&&Error.captureStackTrace(a);throw a;}function p(){var a=new q;a.f=s("ya",ea);a.va="";a.qa="";a.N=[];h(a)}var u={d:0};

<snapped>

y.push(function(){x.fb=j;x.eb=j;x.gb=j});y.push(function(){x.Ta=j;x.Sa=j;x.Ra=j;x.Wa=j;x.Va=j;x.Ua=j});(function(a,b){if(!A){var c=new ya;oa=c;sa(c,function(){a(b)});Ea();x=c}})(function(){return qb()(1,u,"Hello world!")},this.arguments?this.arguments.slice?[].concat(this.arguments.slice()):this.arguments:[]);
$

Why is the javascript code which was generated by a dart compiler so huge?

What problem are they trying to solve by generating such huge javascript files?

Side Note: The javascript files were so huge, SO threw the following error:

Oops! Your question couldn't be submitted because: body is limited to 30000 characters; you entered 140984

Answer 1

What problem are they trying to solve by generating such huge javascript files?

The problem of balancing Dart to be optimal in the majority of cases, rather than just this one personal, specific, contrived, useless example program that nobody would ever seriously try to use in a production project.

Answer 2

If you would like to get even a better JavaScript, try the Frog compiler instead of DartC. Frog ist written in Dart itself.

http://turbomanage.wordpress.com/2011/12/09/dart-dev-mode-cometh/

Note, this blogpost above is a bit outdated. You can meanwhile use the Dart SDK for Frog: http://gsdview.appspot.com/dart-editor-archive-continuous/3058/

This post might also be of interest for you, Seth shows how the Frog generated JS looks like: http://blog.sethladd.com/2011/12/10-lessons-from-porting-javascript-to.html

Here is how you can enable Frog in current Editor: https://groups.google.com/a/dartlang.org/group/misc/msg/5dfe04c69ed0fed3

Answer 3

Why is the javascript code which was generated from a dart code by a dart compiler is so huge?

Because it includes a Dart runtime.

What problem are they trying to solve by generating such huge javascript files?

The problem of running code that is not JavaScript in a browser.