Deno Run TypeScript: A Comprehensive Guide

Table of Contents

1. Fundamental Concepts
2. Usage Methods
3. Common Practices
4. Best Practices
5. Conclusion
6. References

Fundamental Concepts

What is Deno?

Deno is a simple, modern, and secure runtime for JavaScript and TypeScript that uses V8 and is built in Rust. It aims to provide a more secure and consistent development experience compared to Node.js. Some of its key features include:

• Secure by default: Deno requires explicit permissions to access files, network, or environment variables.
• First - class TypeScript support: It can directly execute TypeScript code without the need for a separate compilation step.
• Built - in tooling: Deno comes with built - in tools for testing, formatting, and linting.

deno run

The deno run command is used to execute a JavaScript or TypeScript file in the Deno runtime. When you run a TypeScript file with deno run, Deno automatically compiles the TypeScript code to JavaScript using its internal TypeScript compiler and then executes the resulting JavaScript code.

Usage Methods

Installation

Before you can use deno run to execute TypeScript code, you need to install Deno. You can install Deno using different methods depending on your operating system:

Using Shell (macOS and Linux)

curl -fsSL https://deno.land/x/install/install.sh | sh

Using PowerShell (Windows)

iwr https://deno.land/x/install/install.ps1 -useb | iex

Basic Usage

Once Deno is installed, you can create a simple TypeScript file, for example, hello.ts:

// hello.ts
const message: string = "Hello, Deno!";
console.log(message);

To run this TypeScript file, use the deno run command:

deno run hello.ts

Deno will automatically compile the TypeScript code and print the output:

Hello, Deno!

Permissions

As mentioned earlier, Deno is secure by default. If your TypeScript code needs to access the file system, network, or environment variables, you need to grant the appropriate permissions. For example, if your code reads a file:

// readFile.ts
import { readTextFile } from "https://deno.land/[email protected]/fs/mod.ts";

const filePath = "test.txt";
const content = await readTextFile(filePath);
console.log(content);

To run this code, you need to grant file read permission:

deno run --allow - read readFile.ts

Common Practices

Importing Modules

Deno uses URLs to import modules. You can import both local and remote modules. For example, to import a local module:

// utils.ts
export function add(a: number, b: number): number {
    return a + b;
}

// main.ts
import { add } from "./utils.ts";

const result = add(2, 3);
console.log(result);

To run main.ts:

deno run main.ts

Using Standard Libraries

Deno comes with a rich set of standard libraries. For example, to use the datetime module from the standard library:

import { format } from "https://deno.land/[email protected]/datetime/mod.ts";

const now = new Date();
const formattedDate = format(now, "yyyy - MM - dd");
console.log(formattedDate);

deno run script.ts

Best Practices

Caching Dependencies

Deno caches remote dependencies automatically. However, you can manually cache dependencies using the deno cache command. This can speed up the development process, especially when you have large or slow - to - download dependencies.

deno cache main.ts

Error Handling

Proper error handling is crucial in any application. In TypeScript code running on Deno, use try...catch blocks to handle errors gracefully. For example:

try {
    const content = await Deno.readTextFile("non - existent.txt");
    console.log(content);
} catch (error) {
    if (error instanceof Deno.errors.NotFound) {
        console.log("The file was not found.");
    } else {
        console.log("An unexpected error occurred:", error);
    }
}

Testing

Deno has built - in support for testing. You can write test cases using the Deno.test function. For example:

// add.test.ts
import { assertEquals } from "https://deno.land/[email protected]/testing/asserts.ts";

function add(a: number, b: number): number {
    return a + b;
}

Deno.test("add function should add two numbers correctly", () => {
    const result = add(2, 3);
    assertEquals(result, 5);
});

To run the tests:

deno test add.test.ts

Conclusion

Deno provides a seamless way to run TypeScript code with its built - in TypeScript support and secure runtime environment. The deno run command is a powerful tool that simplifies the process of executing TypeScript files. By understanding the fundamental concepts, usage methods, common practices, and best practices, you can develop efficient and secure TypeScript applications using Deno.

References

• Deno Official Documentation
• Deno Standard Library

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