Typescript - How to create an empty typed array|object |Interface|string with examples

In this short tutorial, Learn how to create an empty typed array in typescript.

It includes multiple ways to create a string-typed empty array.

Let us declare Employee Interface in ts file.

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

Create an empty typed array interface or class

Employee object holds different types of data. The empty typed array is created in many ways.

Using generics type declaration

First, array variable can be declared with a generic array of Employees by assigning an empty array

let employees: Array<Employee> = [];

Thus, create a variable store’s empty typed array.

type assertion

`type assertion is like assigning an object of one type to a variable. This will have no performance impact at runtime. however, It can be used to avoid errors at compile time.

Declared with two syntaxes. the first as syntax and the second is angle-bracket syntax.

The following is an example for creating an empty typed array with as syntax.

let empArray1 = [] as Employee[];

The above syntax can also be written with angle-bracket syntax as follows

let empArray = <Employee[]>[]; 

Both are equal in terms of usage and performance.

Array constructor

Finally, array constructors are generic usage and used by every developer. It uses a new operator to create an empty array.

let empArray = new Array<Employee>(); 
let empArray: Array<Employee> = new Array<Employee>();

It looks good in readability, however, performance impacts creating a reference in memory.

How to create an empty typed string array with examples

There are many ways typed string array’s created with the following syntaxes.

let emptyStringArray: string[] = [];
let emptyStringArray1 = new Array<string>(); 
let emptyStringArray2: Array<string> = new Array<string>();

Steps:

• The first line is with inline empty array initialization
• The second line is a Create using a new keyword
• The third line is an Array with a new object

Create and initialize typed empty objects in an array

In this example, Let’s create a non-empty array with object data that is empty or default values.

let us declare an interface for User

interface User {
  name: string;
  id: number;
  password: string;
}

Following is an example with array initialized with three empty user objects. Partial in typescript allows you to construct object with optional fields Partial<User> return User with optional id,name and password

users: Partial<User>[] = [{}, {}, {}];

And other option is to manual set values for each object with default values of an object

users1: User[] = [{ id: null, name: null, password:null }{ id: null, name: null, password:null }]

Conclusion

To sum up, you learned different ways to create a typed empty array. And also how to create an array with empty objects.

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