您可以通过在处理程序上定义 set 方法来解决此错误:

You can fix this erro by defining a set method on your handler:

set(target, property, value, receiver) {
    target[property] = value;
}

此错误的原因似乎有点奇怪. CanvasRenderingContext2D 实例没有自己的 strokeStyle 属性.相反， CanvasRenderingContext2DPrototype (每个 CanvasRenderingContext2D 实例的原型)具有访问器属性，其 set / get 组件将设置并获取实例的笔触样式值:

The reason for this error might seem a bit strange. CanvasRenderingContext2D instances don't have their own strokeStyle property. Instead, the CanvasRenderingContext2DPrototype (the prototype of every CanvasRenderingContext2D instance) has an accessor property whose set/get components will set and get the stroke-style value for the instance:

> ctx.hasOwnProperty("strokeStyle")
false

> Object.getOwnPropertyDescriptor(ctx.__proto__, "strokeStyle")
Object { get: strokeStyle(), set: strokeStyle(), enumerable: true, configurable: true }

((如果您有兴趣了解有关此模式的更多信息，请查看我对 JSON.parse的回答，不会在循环中出错)对象.)

(If you're interested in learning more about this pattern, have a look at my answer on JSON.parse not erroring on cyclic objects.)

这里的问题是提供给 CanvasRenderingContext2DPrototype.strokeStyle 设置器的 this 是 proxy 对象，而不是实际的 ctx对象.也就是说，当我们仅在代理服务器上设置属性时:

The problem here is that the this supplied to the CanvasRenderingContext2DPrototype.strokeStyle setter is the proxy object, not the actual ctx object. That is, when we set a property on the proxy only:

proxy.isAFake = true;

并在重新定义的设置器中对其进行测试:

and test for it in a redefined setter:

Object.defineProperty(ctx.__proto__, "strokeStyle", {
    set: function() {
        console.log("strokeStyle setter called for proxy?", this.isAFake);
    }
});

我们看到设置器记录了仅代理属性: strokeStyle设置器调用了代理吗?是.

We see the setter logs the proxy-only property: strokeStyle setter called for proxy? true.

无论出于何种原因， CanvasRenderingContext2DPrototype.strokeStyle 上的设置器将仅接受真正的 CanvasRenderingContext2D 实例，而不接受代理实例.

For whatever reason, the setter on CanvasRenderingContext2DPrototype.strokeStyle will accept only a genuine CanvasRenderingContext2D instance, not a proxied one.