What does Dart's output look like?

Question

Dart, Google's new web language, says it supports outputting to JavaScript.

What does a simple conversion look like?

Answer 1

main() {       print('Hello, Dart!'); } 

When compiled with dart2js (as of 2013-04-26) (see note at bottom) it is converted into:

// Generated by dart2js, the Dart to JavaScript compiler. // The code supports the following hooks: // dartPrint(message)   - if this function is defined it is called //                        instead of the Dart [print] method. // dartMainRunner(main) - if this function is defined, the Dart [main] //                        method will not be invoked directly. //                        Instead, a closure that will invoke [main] is //                        passed to [dartMainRunner]. function Isolate() {} init();  var $ = Isolate.$isolateProperties; // Bound closures $.Primitives_printString = function(string) {   if (typeof dartPrint == "function") {     dartPrint(string);     return;   }   if (typeof window == "object") {     if (typeof console == "object")       console.log(string);     return;   }   if (typeof print == "function") {     print(string);     return;   }   throw "Unable to print message: " + String(string); };  $.main = function() {   $.Primitives_printString("Hello, Dart!"); };  $.String = {builtin$cls: "String"};  var $ = null; Isolate = Isolate.$finishIsolateConstructor(Isolate); var $ = new Isolate(); // BEGIN invoke [main]. if (typeof document !== "undefined" && document.readyState !== "complete") {   document.addEventListener("readystatechange", function () {     if (document.readyState == "complete") {       if (typeof dartMainRunner === "function") {         dartMainRunner(function() { $.main(); });       } else {         $.main();       }     }   }, false); } else {   if (typeof dartMainRunner === "function") {     dartMainRunner(function() { $.main(); });   } else {     $.main();   } } // END invoke [main]. function init() {   Isolate.$isolateProperties = {};   Isolate.$finishIsolateConstructor = function(oldIsolate) {     var isolateProperties = oldIsolate.$isolateProperties;     isolateProperties.$currentScript = typeof document == "object" ? document.currentScript || document.scripts[document.scripts.length - 1] : null;     var isolatePrototype = oldIsolate.prototype;     var str = "{\n";     str += "var properties = Isolate.$isolateProperties;\n";     var hasOwnProperty = Object.prototype.hasOwnProperty;     for (var staticName in isolateProperties) {       if (hasOwnProperty.call(isolateProperties, staticName)) {         str += "this." + staticName + "= properties." + staticName + ";\n";       }     }     str += "}\n";     var newIsolate = new Function(str);     newIsolate.prototype = isolatePrototype;     isolatePrototype.constructor = newIsolate;     newIsolate.$isolateProperties = isolateProperties;     return newIsolate;   }; } //@ sourceMappingURL=out.js.map 

Note for posterity: The original answer to this question has been modified to reflect the current state of affairs.

On 2012-05-12 the dart output for Hello World was 18,718 characters.

On 2012-08-29 the output was 1531 characters.

On 2013-04-26, the output was 2642 characters.

dart2js can minify code. Here is an example (as of 2013-04-26)

// Generated by dart2js, the Dart to JavaScript compiler. function I(){} init() var $=I.p $.ib=function(a){if(typeof dartPrint=="function"){dartPrint(a) return}if(typeof window=="object"){if(typeof console=="object")console.log(a) return}if(typeof print=="function"){print(a) return}throw "Unable to print message: " + String(a)} $.E2=function(){$.ib("Hello, Dart!")} $.qU={builtin$cls:"qU"}  var $=null I = I.$finishIsolateConstructor(I) var $=new I() if (typeof document !== "undefined" && document.readyState !== "complete") {   document.addEventListener("readystatechange", function () {     if (document.readyState == "complete") {       if (typeof dartMainRunner === "function") {         dartMainRunner(function() { $.E2(); });       } else {         $.E2();       }     }   }, false); } else {   if (typeof dartMainRunner === "function") {     dartMainRunner(function() { $.E2(); });   } else {     $.E2();   } } function init(){I.p={} I.$finishIsolateConstructor=function(a){var z=a.p z.$currentScript=typeof document=="object"?document.currentScript||document.scripts[document.scripts.length-1]:null var y=a.prototype var x="{\n" x+="var properties = I.p;\n" var w=Object.prototype.hasOwnProperty for(var v in z){if(w.call(z,v)){x+="this."+v+"= properties."+v+";\n"}}x+="}\n" var u=new Function(x) u.prototype=y y.constructor=u u.p=z return u}}//@ sourceMappingURL=out.js.map 

On 2013-04-26, the minified code was 1386 characters.