How to Import another TypeScript Files ?
Last Updated :
02 Mar, 2020
Some times we want some facility that we have been used in our previous projects, in that situation we can’t rewrite that script again we can simply import that by making that file exportable. To import other TypeScript files into an existing TypeScript file we should know the concept of modules. Starting with ECMAScript 2015, JavaScript has a concept of modules and TypeScript shares this concept.
Modules are small units of independent, reusable code that is desired to be used as the building blocks. Modules let the developer define private and public members separately, making it one of the more desired design patterns in the script paradigm. You may see modules as Classes as in any other Object-Oriented Programming Language. Exported from a different module, it has to be imported using one of the import forms.
Example 1: Import a class from a file to another file.
- Code 1: This code file will be imported and save the file name as exportedFile.ts in a directory.
export class exportedFile {
sayHello(user){
return "Hello " + user+ "!" ;
}
}
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- Code 2: This code file will be import the above code, and save this file as the name mainFile.ts in the same directory.
import { exportedFile } from "./exportedFile" ;
let user = new exportedFile();
console.log(user.sayHello( "Geek" ));
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- Output:
Hello Geek!
Note: You have to compile the mainFile.ts that will generate the mainFile.js that run js file.
In the TypeScript file which is to be imported must include an export form and the main file where the class is imported must contain an import form, by which TypeScript can identify the file which is used. By using this type of export and import forms we can import classes, interfaces, functions, variables anything that we want.
Example 2: We can also import them by renaming them as of our needs. Importing a function from another file by renaming the function.
- Code 1: Save this file as a exportedFile.ts
export function sayHello(user:string) {
return "Hello " + user + "!" ;
}
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- Code 2: Save this file as a mainFile.ts
import { sayHello as hello } from "./exportedFile" ;
let user = "Jake" ;
console.log(hello(user));
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- Output:
Hello Jake!
Example 3: We can import all the contents of a file by using import all form as shown below. Import all is indicated as ‘import *’.
Note: To import all, it is necessary to rename the module. It is basically wrapping all the class, function, interface in a single module when we are using the as keyword. We can also import multiple files by simply writing multiple import forms and module location.
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