The digest() method of the SubtleCrypto interface generates a digest of the given data. A digest is a short fixed-length value derived from some variable-length input. Cryptographic digests should exhibit collision-resistance, meaning that it's hard to come up with two different inputs that have the same digest value.
It takes as its arguments an identifier for the digest algorithm to use and the data to digest. It returns a Promise which will be fulfilled with the digest.
Note that this API does not support streaming input: you must read the entire input into memory before passing it into the digest function.
Digest algorithms, also known as cryptographic hash functions, transform an arbitrarily large block of data into a fixed-size output, usually much shorter than the input. They have a variety of applications in cryptography.
This example encodes a message, then calculates its SHA-256 digest and logs the digest length:
js
const text ="An obscure body in the S-K System, your majesty. The inhabitants refer to it as the planet Earth.";asyncfunctiondigestMessage(message){const encoder =newTextEncoder();const data = encoder.encode(message);const hash =await crypto.subtle.digest("SHA-256", data);return hash;}digestMessage(text).then((digestBuffer)=>
console.log(digestBuffer.byteLength),);
Converting a digest to a hex string
The digest is returned as an ArrayBuffer, but for comparison and display digests are often represented as hex strings. This example calculates a digest, then converts the ArrayBuffer to a hex string:
js
const text ="An obscure body in the S-K System, your majesty. The inhabitants refer to it as the planet Earth.";asyncfunctiondigestMessage(message){const msgUint8 =newTextEncoder().encode(message);// encode as (utf-8) Uint8Arrayconst hashBuffer =await crypto.subtle.digest("SHA-256", msgUint8);// hash the messageconst hashArray = Array.from(newUint8Array(hashBuffer));// convert buffer to byte arrayconst hashHex = hashArray
.map((b)=> b.toString(16).padStart(2,"0")).join("");// convert bytes to hex stringreturn hashHex;}digestMessage(text).then((digestHex)=> console.log(digestHex));