是否可以在不使用eval的情况下在JavaScript中实现动态作用域？

是否可以在不使用eval的情况下在JavaScript中实现动态作用域？

属性查找贯穿原型链，与动态范围非常匹配。只需传递您自己的动态范围变量环境即可使用，而不是使用Javascript的词法作用域。

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// Polyfill for older browsers.  Newer ones already have Object.create.if (!Object.create) {  // You don't need to understand this, but  Object.create = function(proto) {    // this constructor does nothing,    function cons() {}    // and we assign it a prototype,    cons.prototype = proto;    // so that the new object has the given proto without any side-effects.    return new cons();  };}

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// Define a new classfunction dyn() {}// with a method which returns a copy-on-write clone of the object.dyn.prototype.cow = function() {  // An empty object is created with this object as its prototype.  Javascript  // will follow the prototype chain to read an attribute, but set new values  // on the new object.  return Object.create(this);}

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// Given an environment, read x then write to it.function g(env) {  console.log(env.x);  env.x = 2;}// Given an environment, write x then call f with a clone.function f(env) {  env.x = 3;  g(env.cow());}

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// Create a new environment.var env = new dyn();// env -> {__proto__: dyn.prototype}// Set a value in it.env.x = 1;// env -> {x: 1}  // Still has dyn.prototype, but it's long so I'll leave it out.f(env.cow());// f()://   env -> {__proto__: {x: 1}}  // Called with env = caller's env.cow()//   > env.x = 3//   env -> {x: 3, __proto__: {x: 1}}  // New value is set in current object//   g()://     env -> {__proto__: {x: 3, __proto__: {x: 1}}}  // caller's env.cow()//     env.x -> 3  // attribute lookup follows chain of prototypes//     > env.x = 2//     env -> {x: 2, __proto__: {x: 3, __proto__: {x: 1}}}console.log(env.x);// env -> {x: 1}  // still unchanged!// env.x -> 1