javascript - 如何在TypeScript中将类型声明为可为空？(How to declare a type as nullable in TypeScript?)

Question

I have an interface in TypeScript.

(我在TypeScript中有一个接口。)

interface Employee{
   id: number;
   name: string;
   salary: number;
}

I would like to make 'salary' as a nullable field (Like we can do in C#).

(我想把'薪水'作为一个可以为空的领域（就像我们在C＃中所做的那样）。)

Is this possible to do in TypeScript?

(这可以在TypeScript中做到吗？)

  ask by Amitabh translate from so

Answer 1

All fields in JavaScript (and in TypeScript) can have the value null or undefined .

(JavaScript（和TypeScript）中的所有字段都可以具有null或undefined值。)

You can make the field optional which is different from nullable.

(您可以将字段设为可选字段，该字段与可空字段不同。)

interface Employee1 {
    name: string;
    salary: number;
}

var a: Employee1 = { name: 'Bob', salary: 40000 }; // OK
var b: Employee1 = { name: 'Bob' }; // Not OK, you must have 'salary'
var c: Employee1 = { name: 'Bob', salary: undefined }; // OK
var d: Employee1 = { name: null, salary: undefined }; // OK

// OK
class SomeEmployeeA implements Employee1 {
    public name = 'Bob';
    public salary = 40000;
}

// Not OK: Must have 'salary'
class SomeEmployeeB implements Employee1 {
    public name: string;
}

Compare with:

(与之比较：)

interface Employee2 {
    name: string;
    salary?: number;
}

var a: Employee2 = { name: 'Bob', salary: 40000 }; // OK
var b: Employee2 = { name: 'Bob' }; // OK
var c: Employee2 = { name: 'Bob', salary: undefined }; // OK
var d: Employee2 = { name: null, salary: 'bob' }; // Not OK, salary must be a number

// OK, but doesn't make too much sense
class SomeEmployeeA implements Employee2 {
    public name = 'Bob';
}