handler.apply()

The following parameters are passed to the apply() method. this is bound to the handler.

target

The target callable object.

thisArg

The this argument for the call.

argumentsList

The list of arguments for the call.

The apply() method can return any value.

The handler.apply() method is a trap for a function call.

This trap can intercept these operations:

• Function call: proxy(...args)
• Function.prototype.apply() and Function.prototype.call()
• Reflect.apply()

Or any other operation that invokes the [[Call]] internal method.

If the following invariants are violated, the trap throws a TypeError when invoked.

• The target must be a callable itself. That is, it must be a function object.

The following code traps a function call.

const p = new Proxy(function () {}, {
  apply(target, thisArg, argumentsList) {
    console.log(`called: ${argumentsList}`);
    return argumentsList[0] + argumentsList[1] + argumentsList[2];
  }
});

console.log(p(1, 2, 3)); // "called: 1,2,3"
                         // 6

• Proxy
• Proxy() constructor
• Function.prototype.apply()
• Function.prototype.call()
• Reflect.apply()