Hashing

Hashing data is a common operation that is facilitated through Deno's support for the Web Crypto API. In addition, the Deno standard library's implementation extends the standard API, allowing for more advanced uses.

In our first example, we'll hash the contents of a string variable.

const message = "The easiest, most secure JavaScript runtime.";

Before we can pass our message to the hashing function, we first need to encode it into a uint8 array.

const messageBuffer = new TextEncoder().encode(message);

Here, we use the built-in crypto.subtle.digest method to hash our original message. The hash is returned as an ArrayBuffer. To obtain a string we'll need to do a little more work.

const hashBuffer = await crypto.subtle.digest("SHA-256", messageBuffer);

We can decode this into a string using the standard library's encodeHex method.

import { encodeHex } from "jsr:@std/encoding/hex";
const hash = encodeHex(hashBuffer);
console.log(hash);

For our second example, we'll hash the contents of a file. Hashing a file is a common operation and doing this without loading the whole file into memory is a typical requirement.

The standard library has extensions to the Web Crypto API that are useful when doing things like hashing a file. These can be accessed through the "crypto" module, a drop-in replacement for the Web Crypto API that delegates to the native implementation when possible.

import { crypto } from "jsr:@std/crypto";
const file = await Deno.open("example.txt", { read: true });

We obtain an async iterable using the readable property.

const readableStream = file.readable;

This time, when we call crypto.subtle.digest, we're using the imported version that allows us to operate on the async iterable.

const fileHashBuffer = await crypto.subtle.digest("SHA-256", readableStream);

Finally, we obtain the hex result using encodeHex like earlier.

const fileHash = encodeHex(fileHashBuffer);
console.log(fileHash);

Run this example locally using the Deno CLI:

deno run --allow-read https://docs.deno.com/examples/hashing.ts

Additional resources: