exactOptionalPropertyTypes设置可选属性不能赋值为undefined。 //打开 exactOptionalPropertyTypesinterfaceMyObj { foo?:'A'|'B'; } let obj:MyObj= { foo:'A'}; obj.foo= undefined;//报错 上面示例中,foo是可选属性,打开exactOptionalPropertyTypes以后,该属性就不能显式赋值为undefined。 16. forceConsiste...
exactOptionalPropertyTypes设置可选属性不能赋值为undefined。 // 打开 exactOptionalPropertyTypes interface MyObj { foo?: 'A' | 'B'; } let obj:MyObj = { foo: 'A' }; obj.foo = undefined; // 报错 上面示例中,foo是可选属性,打开exactOptionalPropertyTypes以后,该属性就不能显式赋值为undefined。
Optional class properties See Optional class properties Example See Example Private and Protected Constructors See Private and Protected Constructors Example See Example Abstract properties and accessors See Abstract properties and accessors Example See Example Implicit index signatures See Implicit index sign...
} type PersonWithOptionalProperties = { [K in keyof Person]?: Person[K] }; const john: Person = { name: 'John', age: 30 }; const johnWithOptionalProperties: PersonWithOptionalProperties = { name: 'John' }; 在此示例中,PersonWithOptionalProperties 是一个映射类型,它使 Person 的所有属性...
classC{ foo:number; bar="hello"; baz:boolean;// ~~~// Error! Property 'baz' has no initializer and is not assigned directly in the constructor.constructor() {this.foo=42; } } In the above,baznever gets set, and TypeScript reports an error. If we truly meant forbazto potentially ...
functionprintValue(value:string|number):void{if(typeofvalue ==='string') {console.log(`The value is a string:${value}`);}elseif(typeofvalue ==='number') {console.log(`The value is a number:${value}`);}}classPerson {name:string;...
在Typescript 4.4 中同时开启--exactOptionalPropertyTypes与--strictNullChecks即可生效。 仔细想想这是合理的,既然定义的类型不是undefined,就算对象是可选类型,也不能认为赋值undefined是合理的,因为age?: number的心理预期是,要么没有这个 key,要么有但是类型为number,所以当Object.keys发现age这个 key 时,值就应该...
In TypeScript there are a few ways to declare an optional object property. You can use a union, like this: // index.ts interface Person { name: string; address: string | undefined; } const john: Person = { name: "John", }; This might look fine, but if you check it out in ...
在TypeScript 4.4 中新加入的标志--exactOptionalPropertyTypes 指定了可选属性类型应完全按照编写的方式来解释,这意味着|undefined 不会添加到类型中: // With 'exactOptionalPropertyTypes' on:constp:Person={name:"Daniel",age:undefined// Error! undefined isn't a number}; ...
classPerson{fullName;// (property) Person.fullName: stringfirstName;// (property) Person.firstName: string | undefinedlastName;// (property) Person.lastName: string | undefinedconstructor(fullName:string){this.fullName=fullName;if(Math.random()){this.firstName=fullName.split(" ")[0];this...