Javascript 代理和 With 语句

Question

为什么会抛出 ReferenceError？

var p = new Proxy({}, {
    get: function(target, name) {
        return `hello world ${name}`;
    }
});
with (p) { console.log(a) }

Uncaught ReferenceError: a is not defined

Answer 1

这段代码很傻。然而，它提出的问题非常有趣。事实证明你可以让它工作!您需要一种方法来使用代理上的 has 方法告诉 javascript 对象中哪些变量可用。此外，由于某些原因，符号不能隐式转换为字符串。因此，为了使此代码“工作”，您需要这样的东西。

var p = new Proxy({}, {
    //we need to identify what elements are available. 
    //this overloads the in operator eg ("foo" in obj)
    has:function(target,name){
        //if we just returned true we would override everything
        //and we need to get to the console
        return name!="console";
    },      
    get: function(target, name) {
        //for some reason the toString is mandatory don't know why 
        //you get "TypeError: Cannot convert a Symbol value to a string" otherwise
        return "Hello world "+name.toString();
    }
});
with (p) { console.log(abc) }