Typescript - 我的属性装饰器不起作用，为什么？

Question

I'm trying to construct custom decorators, for example, a decorator to validate the minimum length of a string.

function Min(limit: number) {
    return function (target: Object, propertyKey: string) {
        let value: string;
        const getter = function () {
            return value;
        };
        const setter = function (newVal: string) {
            if (newVal.length < limit) {
                Object.defineProperty(target, 'errors', {
                    value: `Your password should be bigger than ${limit}`
                });
            }
            else {
                value = newVal;
            }
        };
        Object.defineProperty(target, propertyKey, {
            get: getter,
            set: setter
        });
    }
}

In the class, I'm calling this way:

export class User {

  @Min(8)
  password: string;
}

However, I'm getting this exception:

tslib_1.__decorate([
        ^

ReferenceError: Min is not defined
    at Object.<anonymous>

My tsconfig.json:

{
  "compilerOptions": {
    "module": "commonjs",
    "declaration": true,
    "removeComments": true,
    "emitDecoratorMetadata": true,
    "experimentalDecorators": true,
    "importHelpers": true,
    "target": "es2017",
    "sourceMap": true,
    "outDir": "./dist",
    "baseUrl": "./",
    "incremental": true
  },
  "exclude": [
    "node_modules",
    "dist"
  ]
}

PS: I know there are libraries, for data validations, like the class-validator, however, I would like to create custom decorators for validations and other features.

Where am I going wrong?

Answer 1

It looks like you forgot to import your decorator. Assuming your structure as following:

- decorator.ts
- index.ts

In decorator.ts :

export function Min(limit: number) {
  // ...
}

In the index.ts :

// Don't forget to import your decorator here
import { Min } from './decorator';

export class User {

  @Min(8)
  password: string;
}