我们说我有一个类Person
,如下所示:
class Person {
constructor(
public firstName: string,
public lastName: string,
public age: number
) {}
}
是否可以覆盖此类中的toString()
方法,因此我可以执行以下操作?
function alertMessage(message: string) {
alert(message);
}
alertMessage(new Person('John', 'Smith', 20));
此覆盖可能如下所示:
public toString(): string {
return this.firstName + ' ' + this.lastName;
}
编辑:这实际上有效。有关详细信息,请参阅下面的答案。
答案 0 :(得分:31)
覆盖toString
有点像预期的那样:
class Foo {
private id: number = 23423;
public toString = () : string => {
return `Foo (id: ${this.id})`;
}
}
class Bar extends Foo {
private name:string = "Some name";
public toString = () : string => {
return `Bar (${this.name})`;
}
}
let a: Foo = new Foo();
// Calling log like this will not automatically invoke toString
console.log(a); // outputs: Foo { id: 23423, toString: [Function] }
// To string will be called when concatenating strings
console.log("" + a); // outputs: Foo (id: 23423)
console.log(`${a}`); // outputs: Foo (id: 23423)
// and for overridden toString in subclass..
let b: Bar = new Bar();
console.log(b); // outputs: Bar { id: 23423, toString: [Function], name: 'Some name' }
console.log("" + b); // outputs: Bar (Some name)
console.log(`${b}`); // outputs: Bar (Some name)
// This also works as wxpected; toString is run on Bar instance.
let c: Foo = new Bar();
console.log(c); // outputs: Bar { id: 23423, toString: [Function], name: 'Some name' }
console.log("" + c); // outputs: Bar (Some name)
console.log(`${c}`); // outputs: Bar (Some name)
有时可能会出现问题的是,无法访问父类的toString
:
console.log("" + (new Bar() as Foo));
将在Bar上运行toString,而不是在Foo上运行。
答案 1 :(得分:6)
正如@Kruga所指出的那样,这个例子实际上似乎在运行时JavaScript中起作用。唯一的问题是TypeScript shows a type error。
TS2345:类型'人物'不能分配给' string'。
类型的参数
要解决此消息,您必须:
.toString()
`${obj}`
或obj + ''
)obj as any
(不推荐,因为您将失去类型安全)