如何在TypeScript中将类型声明为可为空? [英] How to declare a type as nullable in TypeScript?
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问题描述
我在TypeScript中有一个界面。
I have an interface in TypeScript.
interface Employee{
id: number;
name: string;
salary: number;
}
我想把'薪水'作为一个可以为空的领域(就像我们可以做C#)。这可以在TypeScript中做到吗?
I would like to make 'salary' as a nullable field (Like we can do in C#). Is this possible to do in TypeScript?
推荐答案
JavaScript(和TypeScript)中的所有字段都可以具有<$ c $的值c> null 或 undefined
。
All fields in JavaScript (and in TypeScript) can have the value null
or undefined
.
您可以使字段可选与nullable不同。
You can make the field optional which is different from nullable.
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;
}
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';
}
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