Javascript - Collection Reflect
Introduction
Reflect is a built-in global object that provides introspection methods.
These methods gather information about the runtime-level meta-operations on objects.
Demo
const restaurant = {
soda: 10, /* www . j a v a 2 s .com*/
beer: 5
};
console.log(Reflect.ownKeys(restaurant));
// ["soda", "beer"]
Result
Reflect is a static object and cannot be used with the new keyword.
For every trap method in ES6 Proxy, there is a matching reflection method available in Reflect.
Reflect is useful for implementing traps in proxies.
The following code are using Reflect with Proxy:
Demo
const restaurant = {
soda: 2, // w w w . j a v a2s .com
beer: 5
};
const restHandler = {
get: function(target, property) {
if (property === "beer") {
return undefined;
}
return Reflect.get(target, property);
}
};
const restProxy = new Proxy(restaurant, restHandler);
console.log(restProxy.beer);
// undefined
console.log(restProxy.soda);
// 2
Result
Here, we are preventing the access to beer and using Reflect.get() to access other properties of the target object.
If Reflect.get is used on a non-object target, it will throw an error, whereas target[property] would return undefined.
It is a good practice to use Reflect.get here.
The following code are trying to get a property on a non-object target:
console.log(Reflect.get(1, "name")); // TypeError: Reflect.get called on non-object console.log(1["name"]); // undefined
Some common useful method from Reflect:
| Method | Description |
|---|---|
| Reflect.get() | A function that returns the value of properties. |
| Reflect.set() | A function that assigns values to properties. Returns a Boolean that is true if the update was successful. |
| Reflect.getPrototypeOf() | Same as Object.getPrototypeOf(). |
| Reflect.has() | The in operator as function. Returns a Boolean indicating whether an own or inherited property exists. |