ES6 类 的 Mixins，用 babel 转译
Mixins for ES6 classes, transpiled with babel
根据各种来源 (2ality, esdiscuss)，应该可以将 mixin 添加到 classes:
EDIT 发现 class 方法不可枚举，因此无法工作。编辑了下面的代码，但仍然没有喜悦
class CartoonCharacter {
constructor(author) {
this.author = author;
}
drawnBy() {
console.log("drawn by", this.author);
}
}
// THIS CANNOT WORK
// class methods are not enumerable
// class Human {
// haveFun() {
// console.log("drinking beer");
// }
// }
let Human = Object.create({}, {
haveFun: {
enumerable: true,
value: function () {
console.log("drinking beer");
}
}
});
class Simpson extends Object.assign(CartoonCharacter, Human) {
constructor(author) {
super(author);
}
}
let homer = new Simpson("Matt Groening");
homer.drawnBy(); // expected: drawn by Matt Groening
homer.haveFun(); // expected: drinking beer
我得到了 "drawn by Matt Groening" 但我得到的不是 "drinking beer" 而是一个错误
-> Uncaught TypeError: E.haveFun is not a function
你的 mixin 有两个问题：
Object.assign 仅复制对象的可枚举属性。但是，class 的方法和属性是不可枚举的。- class 的方法和属性未在构造函数中定义。它们是在构造函数的原型上定义的。
这就是使用 mixins 扩展 class 的方式：
class CartoonCharacter {
constructor(author) {
this.author = author;
}
drawnBy() {
console.log("drawn by", this.author);
}
}
class Human {
haveFun() {
console.log("drinking beer");
}
}
mixin(CartoonCharacter, Human);
class Simpson extends CartoonCharacter {
constructor(author) {
super(author);
}
}
let homer = new Simpson("Matt Groening");
homer.drawnBy(); // expected: drawn by Matt Groening
homer.haveFun(); // expected: drinking beer
function mixin(target, source) {
target = target.prototype; source = source.prototype;
Object.getOwnPropertyNames(source).forEach(function (name) {
if (name !== "constructor") Object.defineProperty(target, name,
Object.getOwnPropertyDescriptor(source, name));
});
}
它在 Babel 中按预期工作：demo。
Subclass 工厂混合
在Javascript中还有另一种实现mixins的方法：使用子class工厂。
子class 工厂是一个函数，除了基class 和return 是该基class 的扩展子class:
const mixin = base => class extends base {
/* properties to mix in */
}
Subclass 工厂是可能的，原因有二：
classes 可以定义为表达式，并且在 Javascriptextends 子句可以包含任意表达式
让我们应用这个模式：
// superclass
class CartoonCharacter {
constructor(author) { this.author = author }
drawnBy() { return "drawn by " + this.author }
}
// mixin 1
const Human = base => class extends base {
haveFun() { return "drinking beer" }
}
// mixin 2
const Simpson = base => class extends base {}
// composed subclass
const Homer = Simpson(Human(CartoonCharacter));
// create an instance
const homer = new Homer("Matt Groening")
console.log(homer.drawnBy());
console.log(homer.haveFun());
sublcass工厂的mixins有什么优势？
- 自然属性优先级：稍后混合在属性中会覆盖先前的同名属性
- mixins (
Human/Simpson) 和 subclasses (Homer) 都可以像往常一样使用 super
- mixins 可以有构造函数（有状态 mixins）
- 原型或实例没有变化
有状态混合
状态使事情变得困难。您应该尽可能避免状态。然而，有时你的 mixin 需要它自己的状态，它是通过构造函数传递的：
class CartoonCharacter {
constructor(author) { this.author = author }
drawnBy() { return "drawn by " + this.author }
}
const Human = base => class extends base {
haveFun() { return "drinking beer" }
}
const Simpson = base => class extends base {
constructor(arg, ...superArgs) {
super(...superArgs);
this.name = arg;
}
sayHey() { return "Hey, I am " + this.name }
}
const Homer = Simpson(Human(CartoonCharacter));
const homer = new Homer("Homer Simpson", "Matt Groening")
console.log(homer.drawnBy());
console.log(homer.haveFun());
console.log(homer.sayHey());
*术语第一个class函数意味着函数可以作为参数或return值像普通数据一样传递
正如@mfeineis、@aadit-m-shah 和@gotofritz 之前讨论过的以及@ftor 的最新 post 所示，人们总是需要仔细考虑 class 将 削弱 进入“mixin”，而不是如何将它们（重新）assemble 进入一个仍然可以被认为是好的设计的层次结构。这些例子只是表明，JavaScript 可能需要比我们已经（被迫）使用的更接近特征的东西。像...
适用Objects/Types
- 不会将他们的语法与 classes,
的语法混合在一起
- 因为它们应该专门在 object/instance 级别工作，因此也来自 (class) 构造函数和其他适用类型的（函数）主体，...
- 因此只是 容器 特征和对象组合规则 将专门在这样的特征处执行/
ApplicableType的申请时间。
为了在实践中证明这样的概念，我确实将上述所有示例重构为 composition of trait from trait 和 object composition from traits inside class 构造函数.
我想讨论这种方法，与当今使用的所有已经接受的技术相比，它的优点和缺点。
// - stateful applicable object/type proxy that does
// link `this` context and injected local state.
//
const withExposeInternalStateProxy = Trait.create(function (use, applicator) {
applicator(function (stateValue) {
this.valueOf = function valueOf () {
return Object.assign({}, stateValue);
};
this.toString = function toString () {
return JSON.stringify(stateValue);
};
});
});
// - applicable object/type that just implements plain behavior.
// - also known as: function based mixin ... kind of "FLight Mixin reloaded".
//
const withHumanBehavior = Trait.create(function (use, applicator) {
function allowWeekness() {
return "allow weekness";
}
function showStrength() {
return "show strength";
}
function thinkFirst() {
return "think first";
}
function drinkingBeer() {
return "drinking beer";
}
applicator(function () {
this.allowWeekness = allowWeekness;
this.showStrength = showStrength;
this.thinkFirst = thinkFirst;
this.drinkingBeer = drinkingBeer;
});
});
// - composite trait that uses its trait composition language ... trait from trait(s).
//
const withStrongBeerDrinkingHabit = Trait.create(function (use, applicator) {
use(withHumanBehavior)
.apply(withHumanBehavior, "drinkingBeer").as("haveFun");
//.apply.all.without("thinkFirst");
//.apply(withHumanBehavior).without("thinkFirst");
});
// - trait that defines a specialized use case of another behavior.
//
const withDoAcceptAlreadyExistingDrinkingHabit = Trait.create(function (use, applicator) {
applicator(function () {
var
type = this;
if (typeof type.haveFun !== "function") {
withStrongBeerDrinkingHabit.call(type);
}
});
});
class CartoonCharacter {
constructor(stateValue) {
// linking `this` context and injected local state.
withExposeInternalStateProxy.call(this, stateValue);
}
drawnBy() {
return ("drawn by " + this.valueOf().author);
}
}
class MaleSimpsonsType extends CartoonCharacter {
constructor(stateValue) {
super(stateValue);
// object/type composition
//
withDoAcceptAlreadyExistingDrinkingHabit.call(super.constructor.prototype);
// withStrongBeerDrinkingHabit.call(super.constructor.prototype); // do not always apply.
//
// withStrongBeerDrinkingHabit.call(this); // nope ...prototype is the far better choice.
}
sayHey() {
return ("Hey, I am " + this.valueOf().name);
}
}
const homer = new MaleSimpsonsType({ name: "Homer Simpson", author: "Matt Groening" });
console.log("\n");
console.log('(homer + "") : ', (homer + ""));
console.log('homer.valueOf() : ', homer.valueOf());
console.log("\n");
console.log('homer.drawnBy() : ', homer.drawnBy());
console.log('homer.haveFun() : ', homer.haveFun());
console.log('homer.sayHey() : ', homer.sayHey());
console.log("\n");
console.log('Object.keys(homer) : ', Object.keys(homer));
console.log('homer.constructor : ', homer.constructor);
console.log('Object.keys(homer.constructor.prototype) : ', Object.keys(homer.constructor.prototype));
console.log('homer.constructor.prototype : ', homer.constructor.prototype);
console.log('(homer instanceof MaleSimpsonsType) : ', (homer instanceof MaleSimpsonsType));
console.log('(homer instanceof CartoonCharacter) : ', (homer instanceof CartoonCharacter));
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为了支持上面的示例，还有另一个线程 - Refactoring legacy mixin-based class hierarchies - 我也借此机会重构了 OP 的给定示例。这个确实具有 after 和 around 对基于普通对象的行为的修改。此处使用的 approach/toolset 确实满足了 OP 的所有要求。现在可以使用 classes，免费封装 state/data，并且对任何类型的方法修改都有状态支持。
根据各种来源 (2ality, esdiscuss)，应该可以将 mixin 添加到 classes:
EDIT 发现 class 方法不可枚举，因此无法工作。编辑了下面的代码，但仍然没有喜悦
class CartoonCharacter {
constructor(author) {
this.author = author;
}
drawnBy() {
console.log("drawn by", this.author);
}
}
// THIS CANNOT WORK
// class methods are not enumerable
// class Human {
// haveFun() {
// console.log("drinking beer");
// }
// }
let Human = Object.create({}, {
haveFun: {
enumerable: true,
value: function () {
console.log("drinking beer");
}
}
});
class Simpson extends Object.assign(CartoonCharacter, Human) {
constructor(author) {
super(author);
}
}
let homer = new Simpson("Matt Groening");
homer.drawnBy(); // expected: drawn by Matt Groening
homer.haveFun(); // expected: drinking beer
我得到了 "drawn by Matt Groening" 但我得到的不是 "drinking beer" 而是一个错误
-> Uncaught TypeError: E.haveFun is not a function
你的 mixin 有两个问题：
Object.assign仅复制对象的可枚举属性。但是，class 的方法和属性是不可枚举的。- class 的方法和属性未在构造函数中定义。它们是在构造函数的原型上定义的。
这就是使用 mixins 扩展 class 的方式：
class CartoonCharacter {
constructor(author) {
this.author = author;
}
drawnBy() {
console.log("drawn by", this.author);
}
}
class Human {
haveFun() {
console.log("drinking beer");
}
}
mixin(CartoonCharacter, Human);
class Simpson extends CartoonCharacter {
constructor(author) {
super(author);
}
}
let homer = new Simpson("Matt Groening");
homer.drawnBy(); // expected: drawn by Matt Groening
homer.haveFun(); // expected: drinking beer
function mixin(target, source) {
target = target.prototype; source = source.prototype;
Object.getOwnPropertyNames(source).forEach(function (name) {
if (name !== "constructor") Object.defineProperty(target, name,
Object.getOwnPropertyDescriptor(source, name));
});
}
它在 Babel 中按预期工作：demo。
Subclass 工厂混合
在Javascript中还有另一种实现mixins的方法：使用子class工厂。
子class 工厂是一个函数，除了基class 和return 是该基class 的扩展子class:
const mixin = base => class extends base {
/* properties to mix in */
}
Subclass 工厂是可能的，原因有二：
classes 可以定义为表达式，并且在 Javascript 中排在第一个 class*
extends子句可以包含任意表达式
让我们应用这个模式：
// superclass
class CartoonCharacter {
constructor(author) { this.author = author }
drawnBy() { return "drawn by " + this.author }
}
// mixin 1
const Human = base => class extends base {
haveFun() { return "drinking beer" }
}
// mixin 2
const Simpson = base => class extends base {}
// composed subclass
const Homer = Simpson(Human(CartoonCharacter));
// create an instance
const homer = new Homer("Matt Groening")
console.log(homer.drawnBy());
console.log(homer.haveFun());
sublcass工厂的mixins有什么优势？
- 自然属性优先级：稍后混合在属性中会覆盖先前的同名属性
- mixins (
Human/Simpson) 和 subclasses (Homer) 都可以像往常一样使用super - mixins 可以有构造函数（有状态 mixins）
- 原型或实例没有变化
有状态混合
状态使事情变得困难。您应该尽可能避免状态。然而，有时你的 mixin 需要它自己的状态，它是通过构造函数传递的：
class CartoonCharacter {
constructor(author) { this.author = author }
drawnBy() { return "drawn by " + this.author }
}
const Human = base => class extends base {
haveFun() { return "drinking beer" }
}
const Simpson = base => class extends base {
constructor(arg, ...superArgs) {
super(...superArgs);
this.name = arg;
}
sayHey() { return "Hey, I am " + this.name }
}
const Homer = Simpson(Human(CartoonCharacter));
const homer = new Homer("Homer Simpson", "Matt Groening")
console.log(homer.drawnBy());
console.log(homer.haveFun());
console.log(homer.sayHey());
*术语第一个class函数意味着函数可以作为参数或return值像普通数据一样传递
正如@mfeineis、@aadit-m-shah 和@gotofritz 之前讨论过的以及@ftor 的最新 post 所示，人们总是需要仔细考虑 class 将 削弱 进入“mixin”，而不是如何将它们（重新）assemble 进入一个仍然可以被认为是好的设计的层次结构。这些例子只是表明，JavaScript 可能需要比我们已经（被迫）使用的更接近特征的东西。像...
适用Objects/Types
- 不会将他们的语法与 classes, 的语法混合在一起
- 因为它们应该专门在 object/instance 级别工作，因此也来自 (class) 构造函数和其他适用类型的（函数）主体，...
- 因此只是 容器 特征和对象组合规则 将专门在这样的特征处执行/
ApplicableType的申请时间。
为了在实践中证明这样的概念，我确实将上述所有示例重构为 composition of trait from trait 和 object composition from traits inside class 构造函数.
我想讨论这种方法，与当今使用的所有已经接受的技术相比，它的优点和缺点。
// - stateful applicable object/type proxy that does
// link `this` context and injected local state.
//
const withExposeInternalStateProxy = Trait.create(function (use, applicator) {
applicator(function (stateValue) {
this.valueOf = function valueOf () {
return Object.assign({}, stateValue);
};
this.toString = function toString () {
return JSON.stringify(stateValue);
};
});
});
// - applicable object/type that just implements plain behavior.
// - also known as: function based mixin ... kind of "FLight Mixin reloaded".
//
const withHumanBehavior = Trait.create(function (use, applicator) {
function allowWeekness() {
return "allow weekness";
}
function showStrength() {
return "show strength";
}
function thinkFirst() {
return "think first";
}
function drinkingBeer() {
return "drinking beer";
}
applicator(function () {
this.allowWeekness = allowWeekness;
this.showStrength = showStrength;
this.thinkFirst = thinkFirst;
this.drinkingBeer = drinkingBeer;
});
});
// - composite trait that uses its trait composition language ... trait from trait(s).
//
const withStrongBeerDrinkingHabit = Trait.create(function (use, applicator) {
use(withHumanBehavior)
.apply(withHumanBehavior, "drinkingBeer").as("haveFun");
//.apply.all.without("thinkFirst");
//.apply(withHumanBehavior).without("thinkFirst");
});
// - trait that defines a specialized use case of another behavior.
//
const withDoAcceptAlreadyExistingDrinkingHabit = Trait.create(function (use, applicator) {
applicator(function () {
var
type = this;
if (typeof type.haveFun !== "function") {
withStrongBeerDrinkingHabit.call(type);
}
});
});
class CartoonCharacter {
constructor(stateValue) {
// linking `this` context and injected local state.
withExposeInternalStateProxy.call(this, stateValue);
}
drawnBy() {
return ("drawn by " + this.valueOf().author);
}
}
class MaleSimpsonsType extends CartoonCharacter {
constructor(stateValue) {
super(stateValue);
// object/type composition
//
withDoAcceptAlreadyExistingDrinkingHabit.call(super.constructor.prototype);
// withStrongBeerDrinkingHabit.call(super.constructor.prototype); // do not always apply.
//
// withStrongBeerDrinkingHabit.call(this); // nope ...prototype is the far better choice.
}
sayHey() {
return ("Hey, I am " + this.valueOf().name);
}
}
const homer = new MaleSimpsonsType({ name: "Homer Simpson", author: "Matt Groening" });
console.log("\n");
console.log('(homer + "") : ', (homer + ""));
console.log('homer.valueOf() : ', homer.valueOf());
console.log("\n");
console.log('homer.drawnBy() : ', homer.drawnBy());
console.log('homer.haveFun() : ', homer.haveFun());
console.log('homer.sayHey() : ', homer.sayHey());
console.log("\n");
console.log('Object.keys(homer) : ', Object.keys(homer));
console.log('homer.constructor : ', homer.constructor);
console.log('Object.keys(homer.constructor.prototype) : ', Object.keys(homer.constructor.prototype));
console.log('homer.constructor.prototype : ', homer.constructor.prototype);
console.log('(homer instanceof MaleSimpsonsType) : ', (homer instanceof MaleSimpsonsType));
console.log('(homer instanceof CartoonCharacter) : ', (homer instanceof CartoonCharacter));
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This expected behavior has not been implemented by the trait that got passed to 'after'."].join(""));else throw new k("Passing identical trait references to both 'apply' and 'after' is a contradiction that violates the composition rules.");else throw new h("Any trait passed to 'after' has to be registered before via 'use'.");else throw new h("'after(<Trait|Function>)' excepts as its sole argument explicitly either a 'Trait' or a 'Function' type.");else throw new n(["\u2026 invalid chaining of '",b,"().after()'"].join(""));else throw new k("Please do not spoof the context of 'use'.");else throw new k("Please do not spoof the context of 'apply'.");return m};L.before=function(c){var b,d,e,f,l,m;if(G(this))if(f=this.valueOf(),m=f.parentLink,w(m))if(e=m.getSetup(),d=e.chainData,b=d.recentCalleeName,v(b,"before"))if(x(c))if(b=m.valueOf(),b=b.traitList,0<=b.indexOf(c))if(b=f.trait,b!==c)if(l=f.methodName,f={},c.call(f),g(f[l]))d.recentCalleeName="before",e.useTraits.rules.push(new A({type:"beforeApply",trait:c,fromTrait:b,methodName:l}));else throw new k(["Please consider applying '",l,"' directly. This expected behavior has not been implemented by the trait that got passed to 'before'."].join(""));else throw new k("Passing identical trait references to both 'apply' and 'before' is a contradiction that violates the composition rules.");else throw new h("Any trait passed to 'before' has to be registered before via 'use'.");else throw new h("'before(<Trait|Function>)' excepts as its sole argument explicitly either a 'Trait' or a 'Function' type.");else throw new n(["\u2026 invalid chaining of '",b,"().before()'"].join(""));else throw new k("Please do not spoof the context of 'use'.");else throw new k("Please do not spoof the context of 'apply'.");return m};L.apply=ha;sa.without=fa;sa.apply=ha;ra.after=function(c){var b,d,e,f;if(w(this))if(e=this.getSetup(),d=e.chainData,b=d.recentCalleeName,v(b,"after"))if(x(c))if(b=this.valueOf(),b=b.traitList,0<=b.indexOf(c))if(b=this.getChild(),f=b.valueOf(),b=f.trait,b!==c)if(f=f.methodName,b={},c.call(b),g(b[f]))d.recentCalleeName="after",e.useTraits.rules.push(new A({type:"afterWrap",trait:c,methodName:f}));else throw new k(["Please consider applying '",f,"' directly. This expected behavior has not been implemented by the trait that got passed to 'after'."].join(""));else throw new k("Passing identical trait references to both 'apply' and 'after' is a contradiction that violates the composition rules.");else throw new h("Any trait passed to 'after' has to be registered before via 'use'.");else throw new h("'after(<Trait|Function>)' excepts as its sole argument explicitly either a 'Trait' or a 'Function' type.");else throw new n(["\u2026 invalid chaining of '",b,"().after()'"].join(""));else throw new k("Please do not spoof the context of 'use'.");return this};ra.before=function(c){var b,d,e,f;if(w(this))if(e=this.getSetup(),d=e.chainData,b=d.recentCalleeName,v(b,"before"))if(x(c))if(b=this.valueOf(),b=b.traitList,0<=b.indexOf(c))if(b=this.getChild(),f=b.valueOf(),b=f.trait,b!==c)if(f=f.methodName,b={},c.call(b),g(b[f]))d.recentCalleeName="before",e.useTraits.rules.push(new A({type:"beforeWrap",trait:c,methodName:f}));else throw new k(["Please consider applying '",f,"' directly. This expected behavior has not been implemented by the trait that got passed to 'before'."].join(""));else throw new k("Passing identical trait references to both 'apply' and 'before' is a contradiction that violates the composition rules.");else throw new h("Any trait passed to 'before' has to be registered before via 'use'.");else throw new h("'before(<Trait|Function>)' excepts as its sole argument explicitly either a 'Trait' or a 'Function' type.");else throw new n(["\u2026 invalid chaining of '",b,"().before()'"].join(""));else throw new k("Please do not spoof the context of 'use'.");return this};A.prototype.execute=function(c,b){var d=this.valueOf();ob[d.type](d,c,b)};return r.Trait={create:function(c){var b,d,e;g(c=F(c))&&(e={chainData:{isTerminated:!1,recentCalleeName:"use"},useTraits:{root:null,rules:[]},applicator:{body:null,proxy:{},root:{},modifiers:[],requires:[],canRequire:!0,didRequire:!1}},b=e.applicator.root,b.requires=cb.bind(e),b.before=Va.bind(e),b.after=Xa.bind(e),b.before.stateful=Wa.bind(e),b.after.stateful=Ya.bind(e),b.afterReturning=Za.bind(e),b.afterThrowing=$a.bind(e),b.afterFinally=ab.bind(e),b.around=bb.bind(e),b=eb.bind(e),d=db.bind(e),c(b,d),e=mb(e));return e},isTrait:qa,isApplicable:x}})(Function("return this")());</script>
为了支持上面的示例，还有另一个线程 - Refactoring legacy mixin-based class hierarchies - 我也借此机会重构了 OP 的给定示例。这个确实具有 after 和 around 对基于普通对象的行为的修改。此处使用的 approach/toolset 确实满足了 OP 的所有要求。现在可以使用 classes，免费封装 state/data，并且对任何类型的方法修改都有状态支持。