Parameter Decorators

function logPosition(target: any, propertyKey: string, parameterIndex: number) {
  console.log(parameterIndex);
}
​
class Cow {
  say(b: string, @logPosition c: boolean) {
    console.log(b);
  }
}
​
new Cow().say('hello', false); // outputs 1 (newline) hello
The above demonstrates decorating method parameters. Readers familiar with Angular can now imagine how Angular implemented their @Inject() system.

Class Decorators

The JavaScript Toolchain

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