import"reflect-metadata";constformat:(formatter:string)=>PropertyDecorator=(formatter)=>{return(target:Object,propertyKey:string|symbol)=>{Reflect.defineMetadata(propertyKey,formatter,target)}}classGreeter{@format("Hello, %s")greeting:string;constructor(message:string){this.greeting=message;}greet(){let...
当前useDefineForClassFields仅在面向 ES5 和更高版本时可用,因为 ES3 中不存在Object.defineProperty。为了实现类似的问题检查,您可以创建一个针对 ES5 的单独项目,并使用它--noEmit来避免进行完整构建。 有关更多信息,您可以查看这个更改的原始 pull request。
This is not a big deal because we can use a “definite assignment assertion“ (!) after the greeting property identifier, but it would be nice for TypeScript to be aware of thesedefinePropertycalls. 🔍 Search Terms constructor, Object.defineProperty, Object.defineProperties, definitely assigned,...
装饰器的实现使用了ES5的 Object.defineProperty 方法,这三个参数也和这个方法的参数一致。装饰器的本质就是一个函数语法糖,通过Object.defineProperty来修改类中一些属性,descriptor参数也是一个对象,是针对key属性的描述符,里面有控制目标对象的该属性是否可写的writable属性等。 访问器装饰器 访问器装饰器声明在一个访...
Object.defineProperty(this, 'idCard', { writable: false }) } } /* runtime */ user.idCard = '321' // everything goes well console.log(user.idCard) // but it's still "123" 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. ...
Object.defineProperty(obj, "x", { value: "hello", writable: false }); obj.x.toLowercase(); // ~~~ // error: // Property 'toLowercase' does not exist on type 'string'. // Did you mean 'toLowerCase'? obj.x = "world"; // ~ // ...
var c = arguments.length, r = c < 3 ? target : desc === null ? desc = Object.getOwnPropertyDescriptor(target, key) : desc, d; if (typeof Reflect === "object" && typeof Reflect.decorate === "function") r = Reflect.decorate(decorators, target, key, desc); ...
valueOf(): Object; /** * Determines whether an object has a property with the specified name. * @param v A property name. */ hasOwnProperty(v: PropertyKey): boolean; /** * Determines whether an object exists in another object's prototype chain. ...
The object type can be anonymous: function greet(person: { name: string; age: number }) { return "Hello " + person.name; } You can also use the interface to define: interface Person { name: string; age: number; } function greet(person: Person) { ...
constobserve=(proto:Object,name:PropertyKey)=>{constkey=Symbol();Object.defineProperty(proto,name,{get(){returnthis[key];},set(v:unknown){this[key]=v;this.onChange?.(name,v);}});};classA{@observefoo='abc';onChange(name:string,v:unknown){console.log(`${name}changed to${v}`);}}...