How to generate SHA-256 hashes in JavaScript

Browser (Web Crypto API): async function sha256(message) { const encoder = new TextEncoder(); const data = encoder.encode(message); const hash = await crypto.subtle.digest('SHA-256', data); return Array.from(new Uint8Array(hash)).map(b => b.toString(16).padStart(2, '0')).join(''); }. Node.js: const crypto = require('crypto'); const hash = crypto.createHash('sha256').update('Hello World').digest('hex'). Note: Web Crypto API is async (returns a Promise); Node.js crypto is synchronous by default.

// JavaScript — generate SHA-256 hash

// Browser (Web Crypto API)
async function sha256(text) {
  const data = new TextEncoder().encode(text);
  const hash = await crypto.subtle.digest("SHA-256", data);
  return Array.from(new Uint8Array(hash))
    .map(b => b.toString(16).padStart(2, "0")).join("");
}
const hash = await sha256("Hello, World!");
console.log(hash);
// "dffd6021bb2bd5b0af676290809ec3a53191dd81c7f70a4b28688a362182986f"

// Node.js
import { createHash } from "crypto";
const hash = createHash("sha256").update("Hello, World!").digest("hex");

SHA-256 hashing patterns in web development

Common use cases: Subresource Integrity (SRI) for script tags — generate a SHA-256 hash of your CDN scripts and add integrity='sha256-...' to prevent tampering. Content hashing for cache busting — hash file contents to generate unique URLs. Webhook verification — HMAC-SHA256 to validate incoming webhooks from Stripe, GitHub, or Slack. In Node.js: const hmac = crypto.createHmac('sha256', secret).update(body).digest('hex'). For client-side, Web Crypto API also supports HMAC: crypto.subtle.sign('HMAC', key, data).

SHA-256 performance in JavaScript

Web Crypto API is significantly faster than pure JavaScript implementations because it uses native C/C++ code under the hood. For Node.js, the built-in crypto module is also native. Avoid pure JS libraries like js-sha256 unless you need compatibility with very old browsers. In Web Workers, crypto.subtle is available for off-main-thread hashing. For hashing large files: read in chunks with FileReader or ReadableStream, and use crypto.subtle.digest() on the complete ArrayBuffer, or use Node.js createHash() with stream.pipe().