How to declare a type as nullable in TypeScript?

Question

I have an interface in TypeScript.

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

I would like to make salary as a nullable field (Like we can do in C#). Is this possible to do in TypeScript?

Answer 1

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

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; } 

Compare with:

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'; }