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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.

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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