Why is my Proxy wrapping a Map's function calls throwing TypeError?

Question

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

cache.set(\'foo\', \'bar\'         


        

Answer 1

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!');
        };
    }
});

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();