为什么我的代理包装Map的函数调用抛出TypeError？ [英] Why is my Proxy wrapping a Map's function calls throwing TypeError?

问题描述

var cache = new Proxy(new Map(), {
    apply: function(target, thisArg, argumentsList) {
        console.log('hello world!');
    }
});

cache.set('foo', 'bar');

据我所知，这个应该结果 hello world！正在登录到控制台，并且地图的 foo 键未设置。但是，当我运行它时，它会抛出：

As far as I can tell this should result in hello world! being logged to the console and the Map's foo key not being set. However, when I run this, it throws:

TypeError: Method Map.prototype.set called on incompatible receiver [object Object]
    at Proxy.set (native)
    at repl:1:7
    at ContextifyScript.Script.runInThisContext (vm.js:23:33)
    at REPLServer.defaultEval (repl.js:340:29)
    at bound (domain.js:280:14)
    at REPLServer.runBound [as eval] (domain.js:293:12)
    at REPLServer.onLine (repl.js:537:10)
    at emitOne (events.js:101:20)
    at REPLServer.emit (events.js:189:7)
    at REPLServer.Interface._onLine (readline.js:238:10)

我已经Googled并将所有的MDN代理文档多次，我不能包围我为什么这不工作。

I've Googled and gone over all the MDN Proxy docs several times, and I can't wrap my head around why this isn't working.

任何想法？我在Node.js 7.5.0上。

Any ideas? I'm on Node.js 7.5.0.

推荐答案

apply 陷阱调用（如果你正在代理一个函数），而不是方法调用（只是属性访问，一个调用，一些这个 shenanigans）。您可以提供 get 并返回一个函数：

apply traps calling (if you were proxying a function), not method calls (which are just property access, a call, and some this shenanigans). You could supply get and return a function instead:

var cache = new Proxy(new Map(), {
    get(target, property, receiver) {
        return function () {
            console.log('hello world!');
        };
    }
});

我不认为你只是想覆盖地图的部分，但是在这种情况下，您可以继承其原型（这是一个比代理更好的选择，如果它是一个选项）：

I don’t suppose you’re just trying to override parts of Map, though? You can inherit from its prototype in that case (this is a much better option than the proxy if it’s an option at all):

class Cache extends Map {
    set(key, value) {
        console.log('hello world!');
    }
}

const cache = new Cache();

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