How to allow classes defined in a module to be accessible outside of a module ?

In typescript by using an import statement, a module can be utilized in another module. any variables, classes, methods, or other objects declared in a module are not accessible outside of it. The keyword “export” may be used to construct a module, and the term “import” can be used to import it into another module. Let’s demonstrate how to do this.

Export: A separate.ts file may be used to create a module, which can have variables, methods, and classes. With all the definitions you intend to include in a module and access from other modules, the prefix export must be used before them. 

The below code is kept in a typescript file called student.ts. This module has two variables and a class called student. The variable section can be used in another module as it is prefixed with the keyword “export” but the student_name variable cannot be accessed in another module as it is not prefixed with the keyword “export”.

Javascript

export let section: number = 9;
export class Student {
    student_id: number;
    name: string;
    constructor(name: string, id: number) {
        this.name = name;
        this.student_id = id;
    }
    displayStudentDetails() {
        console.log(
            "student_id: " + `${this.student_id}` + ",
                Student Name: " + this.name
        );
    }
}

let student_name: string = "aditi";

Import: Variables, classes, etc.. can be accessed from the other class by the current module using the “import” keyword.

Syntax:

Import { name_of_the_class_or_variable_being_exported } from "file_path"
file_path : file path should be specified without any extension.

we can import only those methods, variables, or classes that are prefixed by the keyword “export”.

Example 1:

• Importing a Module’s Single Export: In this example, class Student is imported from the student.ts module. no other variables which are from student.ts get imported. This file can be named studentImport.ts. 

Javascript

import { Student } from "./student";

let Object = new Student("richa", 61);
console.log(Object.displayStudentDetails());

Output:

student_id: 61, Student Name: richa

• Importing the entire module: In this example, we import all the exports from the module. The * syntax is used to import all the exports from the previous module. 

Javascript

import * as stu from "./student";

let Object = new stu.Student("richa", 61);
console.log(Object.displayStudentDetails());

let variable = stu.section;
console.log(variable);

Output:

student_id: 61, Student Name: richa
undefined
9

What if we try importing student_name which is not prefixed with keyword export?. typescript compiler raises an error. 

Javascript

import * as stu from "./student";

// let Object = new stu.Student("richa", 61);
// console.log(Object.displayStudentDetails());

let variable = stu.student_name;
console.log(variable);

Output:

error TS2339: Property 'student_name' does not exist on type 'typeof import("/Users/...")'.
6 let variable = stu.student_name;

Changing the name of a module’s export: Here, ‘as’ keyword is used to change the name of the export. Sometimes we’d like to rename our exports to much simpler names, in such cases we can rename exports as given in the below example. This code is in studentImport.ts. 

Javascript

import { Student as S } from "./three";

let Object = new S("richa", 61);
console.log(Object.displayStudentDetails());

Output:

student_id: 61, Student Name: richa
undefined

Note on compilation: First the typescript file which has the import statements must be compiled in the terminal.

tsc studentImport.ts

Then the javascript file created must be compiled using the below command:

node studentImport.js