@rbxts/jsnatives

Proxy - apply hook

The apply hook is triggered when a proxy is called as a function.

Signature

function apply<T>(target: T, proxy: T, ...args: unknown[]): any;

Description

The apply handler trap is called when the proxy is invoked as a function. It allows you to intercept function call operations.

Parameters

target: The original target object the proxy is wrapping
proxy: The proxy instance itself
...args: The arguments passed to the function

Return value

Any value that should be returned from the function call

Examples

Basic function call interception

const target = function(x, y) {
  return x + y;
};

const proxy = new Proxy(target, {
  apply: (target, proxy, ...args) => {
    console.log(`Function called with arguments: ${args.join(", ")}`);
    return target(...args);
  }
});

console.log(proxy(1, 2)); // Logs: "Function called with arguments: 1, 2", then 3

Function call transformation

const multiply = function(x, y) {
  return x * y;
};

const proxy = new Proxy(multiply, {
  apply: (target, proxy, ...args) => {
    // Double the result
    return target(...args) * 2;
  }
});

console.log(proxy(2, 3)); // 12 (2 * 3 * 2)

Function call validation

const divide = function(x, y) {
  return x / y;
};

const safeDivide = new Proxy(divide, {
  apply: (target, proxy, ...args) => {
    if (args[1] === 0) {
      throw new Error("Cannot divide by zero");
    }
    return target(...args);
  }
});

console.log(safeDivide(10, 2)); // 5
// safeDivide(10, 0); // Throws: "Cannot divide by zero"

Method profiling

const calculator = {
  add: function(x, y) { return x + y; },
  subtract: function(x, y) { return x - y; },
  multiply: function(x, y) { return x * y; }
};

const profiledCalculator = new Proxy(calculator, {
  get: (target, prop, proxy) => {
    const value = target[prop];

    if (typeof value === "function") {
      return new Proxy(value, {
        apply: (fn, thisArg, ...args) => {
          console.time(`${String(prop)} operation`);
          const result = fn.apply(target, args[0]);
          console.timeEnd(`${String(prop)} operation`);
          return result;
        }
      });
    }

    return value;
  }
});

profiledCalculator.add(1, 2); // Logs: "add operation: 0.123ms"
profiledCalculator.multiply(3, 4); // Logs: "multiply operation: 0.045ms"