dart - 使用 dart 创建一个 javascript 库

Question

问题
我目前正在开发一个 JavaScript 库，为了减少错误数量，我认为我的库可能会从使用 Dart 的静态类型机制中受益。首先，因为我的库既没有与 HTML 也没有与其他 JavaScript 库进行任何互操作，只有纯 javascript 对象操作的东西。但是，我没有在网上找到任何信息显示如何使用 dart 构建 JS 库。所以我自己尝试这样做，创建了初始 dart 文件:

library Repo;

class Type {
  final String name;
  final TypeCategory category;
  
  Type(String name, TypeCategory category) : name = name, category = category {
    category.types[name] = this;
  }
}

class TypeCategory {
  final String name;
  final Map<String, Type> types = new Map();
  
  TypeCategory(this.name);
}

class Branch {
  
}

class Descriptor {
  
}

class TableDescriptor extends Descriptor {
  TableDescriptor.ctor() {
    
  }
}

class Repo {
  Descriptor descriptor(String name) {
    
  }
  
  Branch branch(String name) {
    
  }
  
  void Merge() {
    
  }
}


main() {
  return Repo;
}

使用 dart2js 将其编译为 JavaScript 以查看我的表现:

// Generated by dart2js, the Dart to JavaScript compiler version: 1.3.6.
// The code supports the following hooks:
// dartPrint(message):
//    if this function is defined it is called instead of the Dart [print]
//    method.
//
// dartMainRunner(main, args):
//    if this function is defined, the Dart [main] method will not be invoked
//    directly. Instead, a closure that will invoke [main], and its arguments
//    [args] is passed to [dartMainRunner].
(function($) {
function dart(){ this.x = 0 }var A = new dart;
delete A.x;
var B = new dart;
delete B.x;
var C = new dart;
delete C.x;
var D = new dart;
delete D.x;
var E = new dart;
delete E.x;
var F = new dart;
delete F.x;
var G = new dart;
delete G.x;
var H = new dart;
delete H.x;
var J = new dart;
delete J.x;
var K = new dart;
delete K.x;
var L = new dart;
delete L.x;
var M = new dart;
delete M.x;
var N = new dart;
delete N.x;
var O = new dart;
delete O.x;
var P = new dart;
delete P.x;
var Q = new dart;
delete Q.x;
var R = new dart;
delete R.x;
var S = new dart;
delete S.x;
var T = new dart;
delete T.x;
var U = new dart;
delete U.x;
var V = new dart;
delete V.x;
var W = new dart;
delete W.x;
var X = new dart;
delete X.x;
var Y = new dart;
delete Y.x;
var Z = new dart;
delete Z.x;
function Isolate() {}
init();

$ = Isolate.$isolateProperties;
var $$ = {};

(function (reflectionData) {
  "use strict";
  function map(x){x={x:x};delete x.x;return x}
    function processStatics(descriptor) {
      for (var property in descriptor) {
        if (!hasOwnProperty.call(descriptor, property)) continue;
        if (property === "^") continue;
        var element = descriptor[property];
        var firstChar = property.substring(0, 1);
        var previousProperty;
        if (firstChar === "+") {
          mangledGlobalNames[previousProperty] = property.substring(1);
          var flag = descriptor[property];
          if (flag > 0) descriptor[previousProperty].$reflectable = flag;
          if (element && element.length) init.typeInformation[previousProperty] = element;
        } else if (firstChar === "@") {
          property = property.substring(1);
          $[property]["@"] = element;
        } else if (firstChar === "*") {
          globalObject[previousProperty].$defaultValues = element;
          var optionalMethods = descriptor.$methodsWithOptionalArguments;
          if (!optionalMethods) {
            descriptor.$methodsWithOptionalArguments = optionalMethods = {}
          }
          optionalMethods[property] = previousProperty;
        } else if (typeof element === "function") {
          globalObject[previousProperty = property] = element;
          functions.push(property);
          init.globalFunctions[property] = element;
        } else if (element.constructor === Array) {
          addStubs(globalObject, element, property, true, descriptor, functions);
        } else {
          previousProperty = property;
          var newDesc = {};
          var previousProp;
          for (var prop in element) {
            if (!hasOwnProperty.call(element, prop)) continue;
            firstChar = prop.substring(0, 1);
            if (prop === "static") {
              processStatics(init.statics[property] = element[prop]);
            } else if (firstChar === "+") {
              mangledNames[previousProp] = prop.substring(1);
              var flag = element[prop];
              if (flag > 0) element[previousProp].$reflectable = flag;
            } else if (firstChar === "@" && prop !== "@") {
              newDesc[prop.substring(1)]["@"] = element[prop];
            } else if (firstChar === "*") {
              newDesc[previousProp].$defaultValues = element[prop];
              var optionalMethods = newDesc.$methodsWithOptionalArguments;
              if (!optionalMethods) {
                newDesc.$methodsWithOptionalArguments = optionalMethods={}
              }
              optionalMethods[prop] = previousProp;
            } else {
              var elem = element[prop];
              if (prop !== "^" && elem != null && elem.constructor === Array && prop !== "<>") {
                addStubs(newDesc, elem, prop, false, element, []);
              } else {
                newDesc[previousProp = prop] = elem;
              }
            }
          }
          $$[property] = [globalObject, newDesc];
          classes.push(property);
        }
      }
    }
  function addStubs(descriptor, array, name, isStatic, originalDescriptor, functions) {
    var f, funcs = [originalDescriptor[name] = descriptor[name] = f = array[0]];
    f.$stubName = name;
    functions.push(name);
    for (var index = 0; index < array.length; index += 2) {
      f = array[index + 1];
      if (typeof f != "function") break;
      f.$stubName = array[index + 2];
      funcs.push(f);
      if (f.$stubName) {
        originalDescriptor[f.$stubName] = descriptor[f.$stubName] = f;
        functions.push(f.$stubName);
      }
    }
    for (var i = 0; i < funcs.length; index++, i++) {
      funcs[i].$callName = array[index + 1];
    }
    var getterStubName = array[++index];
    array = array.slice(++index);
    var requiredParameterInfo = array[0];
    var requiredParameterCount = requiredParameterInfo >> 1;
    var isAccessor = (requiredParameterInfo & 1) === 1;
    var isSetter = requiredParameterInfo === 3;
    var isGetter = requiredParameterInfo === 1;
    var optionalParameterInfo = array[1];
    var optionalParameterCount = optionalParameterInfo >> 1;
    var optionalParametersAreNamed = (optionalParameterInfo & 1) === 1;
    var isIntercepted = requiredParameterCount + optionalParameterCount != funcs[0].length;
    var functionTypeIndex = array[2];
    var unmangledNameIndex =  2 * optionalParameterCount + requiredParameterCount + 3;
    var isReflectable = array.length > unmangledNameIndex;

    if (getterStubName) {
      f = tearOff(funcs, array, isStatic, name, isIntercepted);
      f.getterStub = true;
      if (isStatic) init.globalFunctions[name] = f;
      originalDescriptor[getterStubName] = descriptor[getterStubName] = f;
      funcs.push(f);
      if (getterStubName) functions.push(getterStubName);
      f.$stubName = getterStubName;
      f.$callName = null;
      if (isIntercepted) init.interceptedNames[getterStubName] = true;
    }
    if (isReflectable) {
      for (var i = 0; i < funcs.length; i++) {
        funcs[i].$reflectable = 1;
        funcs[i].$reflectionInfo = array;
      }
      var mangledNames = isStatic ? init.mangledGlobalNames : init.mangledNames;
      var unmangledName = array[unmangledNameIndex];
      var reflectionName = unmangledName;
      if (getterStubName) mangledNames[getterStubName] = reflectionName;
      if (isSetter) {
        reflectionName += "=";
      } else if (!isGetter) {
        reflectionName += ":" + requiredParameterCount + ":" + optionalParameterCount;
      }
      mangledNames[name] = reflectionName;
      funcs[0].$reflectionName = reflectionName;
      funcs[0].$metadataIndex = unmangledNameIndex + 1;
      if (optionalParameterCount) descriptor[unmangledName + "*"] = funcs[0];
    }
  }
  function tearOffGetterNoCsp(funcs, reflectionInfo, name, isIntercepted) {
    return isIntercepted
        ? new Function("funcs", "reflectionInfo", "name", "H", "c",
            "return function tearOff_" + name + (functionCounter++)+ "(x) {" +
              "if (c === null) c = H.closureFromTearOff(" +
                  "this, funcs, reflectionInfo, false, [x], name);" +
              "return new c(this, funcs[0], x, name);" +
            "}")(funcs, reflectionInfo, name, H, null)
        : new Function("funcs", "reflectionInfo", "name", "H", "c",
            "return function tearOff_" + name + (functionCounter++)+ "() {" +
              "if (c === null) c = H.closureFromTearOff(" +
                  "this, funcs, reflectionInfo, false, [], name);" +
              "return new c(this, funcs[0], null, name);" +
            "}")(funcs, reflectionInfo, name, H, null)
  }
  function tearOffGetterCsp(funcs, reflectionInfo, name, isIntercepted) {
    var cache = null;
    return isIntercepted
        ? function(x) {
            if (cache === null) cache = H.closureFromTearOff(this, funcs, reflectionInfo, false, [x], name);
            return new cache(this, funcs[0], x, name)
          }
        : function() {
            if (cache === null) cache = H.closureFromTearOff(this, funcs, reflectionInfo, false, [], name);
            return new cache(this, funcs[0], null, name)
          }
  }
  function tearOff(funcs, reflectionInfo, isStatic, name, isIntercepted) {
    var cache;
    return isStatic
        ? function() {
            if (cache === void 0) cache = H.closureFromTearOff(this, funcs, reflectionInfo, true, [], name).prototype;
            return cache;
          }
        : tearOffGetter(funcs, reflectionInfo, name, isIntercepted);
  }
  var functionCounter = 0;
  var tearOffGetter = (typeof dart_precompiled == "function")
      ? tearOffGetterCsp : tearOffGetterNoCsp;
  if (!init.libraries) init.libraries = [];
  if (!init.mangledNames) init.mangledNames = map();
  if (!init.mangledGlobalNames) init.mangledGlobalNames = map();
  if (!init.statics) init.statics = map();
  if (!init.typeInformation) init.typeInformation = map();
  if (!init.globalFunctions) init.globalFunctions = map();
  if (!init.interceptedNames) init.interceptedNames = map();
  var libraries = init.libraries;
  var mangledNames = init.mangledNames;
  var mangledGlobalNames = init.mangledGlobalNames;
  var hasOwnProperty = Object.prototype.hasOwnProperty;
  var length = reflectionData.length;
  for (var i = 0; i < length; i++) {
    var data = reflectionData[i];
    var name = data[0];
    var uri = data[1];
    var metadata = data[2];
    var globalObject = data[3];
    var descriptor = data[4];
    var isRoot = !!data[5];
    var fields = descriptor && descriptor["^"];
    var classes = [];
    var functions = [];
    processStatics(descriptor);
    libraries.push([name, uri, classes, functions, metadata, fields, isRoot,
                    globalObject]);
  }
})
([
["Repo", "repo.dart", , F, {
  "^": "",
  main: function() {
    return C.Type_Jeh;
  }
},
1],
["_js_helper", "dart:_js_helper", , H, {
  "^": "",
  createRuntimeType: function($name) {
    return new H.TypeImpl($name, null);
  },
  TypeImpl: {
    "^": "Object;_typeName,_unmangledName"
  }
}],
["dart.core", "dart:core", , P, {
  "^": "",
  Null: {
    "^": "Object;"
  },
  Object: {
    "^": ";"
  }
}],
]);
Isolate.$finishClasses($$, $, null);
$$ = null;

// Runtime type support
// getInterceptor methods
C.Type_Jeh = H.createRuntimeType('Repo');
$.libraries_to_load = {};
$.Closure_functionCounter = 0;
$.BoundClosure_selfFieldNameCache = null;
$.BoundClosure_receiverFieldNameCache = null;

init.functionAliases = {};
;
init.metadata = [];
$ = null;
Isolate = Isolate.$finishIsolateConstructor(Isolate);
$ = new Isolate();
function convertToFastObject(properties) {
  function MyClass() {};
  MyClass.prototype = properties;
  new MyClass();
  return properties;
}
A = convertToFastObject(A);
B = convertToFastObject(B);
C = convertToFastObject(C);
D = convertToFastObject(D);
E = convertToFastObject(E);
F = convertToFastObject(F);
G = convertToFastObject(G);
H = convertToFastObject(H);
J = convertToFastObject(J);
K = convertToFastObject(K);
L = convertToFastObject(L);
M = convertToFastObject(M);
N = convertToFastObject(N);
O = convertToFastObject(O);
P = convertToFastObject(P);
Q = convertToFastObject(Q);
R = convertToFastObject(R);
S = convertToFastObject(S);
T = convertToFastObject(T);
U = convertToFastObject(U);
V = convertToFastObject(V);
W = convertToFastObject(W);
X = convertToFastObject(X);
Y = convertToFastObject(Y);
Z = convertToFastObject(Z);
// BEGIN invoke [main].
;(function (callback) {
  if (typeof document === "undefined") {
    callback(null);
    return;
  }
  if (document.currentScript) {
    callback(document.currentScript);
    return;
  }

  var scripts = document.scripts;
  function onLoad(event) {
    for (var i = 0; i < scripts.length; ++i) {
      scripts[i].removeEventListener("load", onLoad, false);
    }
    callback(event.target);
  }
  for (var i = 0; i < scripts.length; ++i) {
    scripts[i].addEventListener("load", onLoad, false);
  }
})(function(currentScript) {
  init.currentScript = currentScript;

  if (typeof dartMainRunner === "function") {
    dartMainRunner(F.main, []);
  } else {
    F.main([]);
  }
});
// END invoke [main].
function init() {
  Isolate.$isolateProperties = {};
  function generateAccessor(fieldDescriptor, accessors, cls) {
    var fieldInformation = fieldDescriptor.split("-");
    var field = fieldInformation[0];
    var len = field.length;
    var code = field.charCodeAt(len - 1);
    var reflectable;
    if (fieldInformation.length > 1)
      reflectable = true;
    else
      reflectable = false;
    code = code >= 60 && code <= 64 ? code - 59 : code >= 123 && code <= 126 ? code - 117 : code >= 37 && code <= 43 ? code - 27 : 0;
    if (code) {
      var getterCode = code & 3;
      var setterCode = code >> 2;
      var accessorName = field = field.substring(0, len - 1);
      var divider = field.indexOf(":");
      if (divider > 0) {
        accessorName = field.substring(0, divider);
        field = field.substring(divider + 1);
      }
      if (getterCode) {
        var args = getterCode & 2 ? "receiver" : "";
        var receiver = getterCode & 1 ? "this" : "receiver";
        var body = "return " + receiver + "." + field;
        var property = cls + ".prototype.get$" + accessorName + "=";
        var fn = "function(" + args + "){" + body + "}";
        if (reflectable)
          accessors.push(property + "$reflectable(" + fn + ");\n");
        else
          accessors.push(property + fn + ";\n");
      }
      if (setterCode) {
        var args = setterCode & 2 ? "receiver, value" : "value";
        var receiver = setterCode & 1 ? "this" : "receiver";
        var body = receiver + "." + field + " = value";
        var property = cls + ".prototype.set$" + accessorName + "=";
        var fn = "function(" + args + "){" + body + "}";
        if (reflectable)
          accessors.push(property + "$reflectable(" + fn + ");\n");
        else
          accessors.push(property + fn + ";\n");
      }
    }
    return field;
  }
  Isolate.$isolateProperties.$generateAccessor = generateAccessor;
  function defineClass(name, cls, fields) {
    var accessors = [];
    var str = "function " + cls + "(";
    var body = "";
    for (var i = 0; i < fields.length; i++) {
      if (i != 0)
        str += ", ";
      var field = generateAccessor(fields[i], accessors, cls);
      var parameter = "parameter_" + field;
      str += parameter;
      body += "this." + field + " = " + parameter + ";\n";
    }
    str += ") {\n" + body + "}\n";
    str += cls + ".builtin$cls=\"" + name + "\";\n";
    str += "$desc=$collectedClasses." + cls + ";\n";
    str += "if($desc instanceof Array) $desc = $desc[1];\n";
    str += cls + ".prototype = $desc;\n";
    if (typeof defineClass.name != "string") {
      str += cls + ".name=\"" + cls + "\";\n";
    }
    str += accessors.join("");
    return str;
  }
  var inheritFrom = function() {
    function tmp() {
    }
    var hasOwnProperty = Object.prototype.hasOwnProperty;
    return function(constructor, superConstructor) {
      tmp.prototype = superConstructor.prototype;
      var object = new tmp();
      var properties = constructor.prototype;
      for (var member in properties)
        if (hasOwnProperty.call(properties, member))
          object[member] = properties[member];
      object.constructor = constructor;
      constructor.prototype = object;
      return object;
    };
  }();
  Isolate.$finishClasses = function(collectedClasses, isolateProperties, existingIsolateProperties) {
    var pendingClasses = {};
    if (!init.allClasses)
      init.allClasses = {};
    var allClasses = init.allClasses;
    var hasOwnProperty = Object.prototype.hasOwnProperty;
    if (typeof dart_precompiled == "function") {
      var constructors = dart_precompiled(collectedClasses);
    } else {
      var combinedConstructorFunction = "function $reflectable(fn){fn.$reflectable=1;return fn};\n" + "var $desc;\n";
      var constructorsList = [];
    }
    for (var cls in collectedClasses) {
      if (hasOwnProperty.call(collectedClasses, cls)) {
        var desc = collectedClasses[cls];
        if (desc instanceof Array)
          desc = desc[1];
        var classData = desc["^"], supr, name = cls, fields = classData;
        if (typeof classData == "string") {
          var split = classData.split("/");
          if (split.length == 2) {
            name = split[0];
            fields = split[1];
          }
        }
        var s = fields.split(";");
        fields = s[1] == "" ? [] : s[1].split(",");
        supr = s[0];
        split = supr.split(":");
        if (split.length == 2) {
          supr = split[0];
          var functionSignature = split[1];
          if (functionSignature)
            desc.$signature = function(s) {
              return function() {
                return init.metadata[s];
              };
            }(functionSignature);
        }
        if (typeof dart_precompiled != "function") {
          combinedConstructorFunction += defineClass(name, cls, fields);
          constructorsList.push(cls);
        }
        if (supr)
          pendingClasses[cls] = supr;
      }
    }
    if (typeof dart_precompiled != "function") {
      combinedConstructorFunction += "return [\n  " + constructorsList.join(",\n  ") + "\n]";
      var constructors = new Function("$collectedClasses", combinedConstructorFunction)(collectedClasses);
      combinedConstructorFunction = null;
    }
    for (var i = 0; i < constructors.length; i++) {
      var constructor = constructors[i];
      var cls = constructor.name;
      var desc = collectedClasses[cls];
      var globalObject = isolateProperties;
      if (desc instanceof Array) {
        globalObject = desc[0] || isolateProperties;
        desc = desc[1];
      }
      allClasses[cls] = constructor;
      globalObject[cls] = constructor;
    }
    constructors = null;
    var finishedClasses = {};
    init.interceptorsByTag = Object.create(null);
    init.leafTags = {};
    function finishClass(cls) {
      var hasOwnProperty = Object.prototype.hasOwnProperty;
      if (hasOwnProperty.call(finishedClasses, cls))
        return;
      finishedClasses[cls] = true;
      var superclass = pendingClasses[cls];
      if (!superclass || typeof superclass != "string")
        return;
      finishClass(superclass);
      var constructor = allClasses[cls];
      var superConstructor = allClasses[superclass];
      if (!superConstructor)
        superConstructor = existingIsolateProperties[superclass];
      var prototype = inheritFrom(constructor, superConstructor);
    }
    for (var cls in pendingClasses)
      finishClass(cls);
  };
  Isolate.$lazy = function(prototype, staticName, fieldName, getterName, lazyValue) {
    var sentinelUndefined = {};
    var sentinelInProgress = {};
    prototype[fieldName] = sentinelUndefined;
    prototype[getterName] = function() {
      var result = $[fieldName];
      try {
        if (result === sentinelUndefined) {
          $[fieldName] = sentinelInProgress;
          try {
            result = $[fieldName] = lazyValue();
          } finally {
            if (result === sentinelUndefined) {
              if ($[fieldName] === sentinelInProgress) {
                $[fieldName] = null;
              }
            }
          }
        } else {
          if (result === sentinelInProgress)
            H.throwCyclicInit(staticName);
        }
        return result;
      } finally {
        $[getterName] = function() {
          return this[fieldName];
        };
      }
    };
  };
  Isolate.$finishIsolateConstructor = function(oldIsolate) {
    var isolateProperties = oldIsolate.$isolateProperties;
    function Isolate() {
      var hasOwnProperty = Object.prototype.hasOwnProperty;
      for (var staticName in isolateProperties)
        if (hasOwnProperty.call(isolateProperties, staticName))
          this[staticName] = isolateProperties[staticName];
      function ForceEfficientMap() {
      }
      ForceEfficientMap.prototype = this;
      new ForceEfficientMap();
    }
    Isolate.prototype = oldIsolate.prototype;
    Isolate.prototype.constructor = Isolate;
    Isolate.$isolateProperties = isolateProperties;
    Isolate.$finishClasses = oldIsolate.$finishClasses;
    return Isolate;
  };
}
})()

//# sourceMappingURL=out.js.map
//@ sourceMappingURL=out.js.map

就是这样，我扔掉了 Dart，因为我不知道如何处理生成的 JS 文件，而且我害怕保持生成的库界面干净并且与我正在使用的界面相似可能需要大量时间使用 JavaScript。
问题

如何公开在 Dart 中创建的类定义，然后在 JavaScript 中使用它们？

当几乎所有潜在的库用户都将使用 JS 版本时，您认为进入 Dart 是否值得？ (由于社区规模的差异，使用 dart 已经不适合我，这意味着更少的人会发现为我的图书馆做出贡献很容易)

在您看来，我该怎么办？

Answer 1

尽管 Dart 支持这个用例，但如果你的目标是 JavaScript 开发人员，我会坚持使用 JavaScript。

@AlexandreArdhuin 在他对 Expose Dart functions to javascript 的回答中显示如何使 JavaScript 可以使用 Dart 函数。
下dart-js-interop有许多示例如何在 Dart 和 JavaScript 之间进行函数调用和传递数据。