TypeScript 覆盖 ToString()

发布于02月12日

假设我有一个Person级的课程，看起来像这样:

class Person {
    constructor(
        public firstName: string,
        public lastName: string,
        public age: number
    ) {}
}

我已经覆盖了toString方法，如下所示.

public toString(): string {
    return this.firstName + ' ' + this.lastName;
}

现在，我希望能够在运行时执行以下操作:

function alertMessage(message: string) {
    alert(message);
}

alertMessage(new Person('John', 'Smith', 20));

但这仍然给了我一个错误:

TS2345:类型为"Person"的参数不能分配给类型为"string"的参数.

我如何给这个string参数赋值Person？

推荐答案

覆盖toString个工程，就像预期的那样:

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 expected; 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)

但有时可能出现的问题是，不可能访问父类的toString: