Class Decorators

  1. function log(prefix?: string) {
  2.   return (target) => {
  3.     // save a reference to the original constructor
  4.     var original = target;
  6.     // a utility function to generate instances of a class
  7.     function construct(constructor, args) {
  8.       var c: any = function () {
  9.         return constructor.apply(this, args);
  10.       }
  11.       c.prototype = constructor.prototype;
  12.       return new c();
  13.     }
  15.     // the new constructor behavior
  16.     var f: any = function (...args) {
  17.       console.log(prefix + original.name);
  18.       return construct(original, args);
  19.     }
  21.     // copy prototype so instanceof operator still works
  22.     f.prototype = original.prototype;
  24.     // return new constructor (will override original)
  25.     return f;
  26.   };
  27. }
  29. @log('hello')
  30. class World {
  31. }
  33. const w = new World(); // outputs "helloWorld"

In the example log is invoked using @, and passed a string as a parameter,@log() returns an anonymous function that is the actual decorator.

The decorator function takes a class, or constructor function (ES5) as anargument. The decorator function then returns a new class constructionfunction that is used whenever World is instantiated.

This decorator does nothing other than log out its given parameter, and itstarget's class name to the console.

原文: https://angular-2-training-book.rangle.io/handout/features/class_decorators.html