Introduction to String Hashing in JavaScript

String hashing is a crucial concept in computer science and web development. It is used extensively in data structures, algorithms, and security. Hashing converts a given string into a fixed-size alphanumeric string, often a hash code. In this blog post, we’ll introduce string hashing in JavaScript and explore various useful APIs with code snippets.

Useful APIs for String Hashing

1. Built-in Hash Functions

JavaScript does not come with built-in string hashing functions, but we can use the crypto library in Node.js.

  const crypto = require('crypto');
  function hashString(str) {
    return crypto.createHash('sha256').update(str).digest('hex');
  }
  console.log(hashString('hello')); // Hash of the string 'hello'

2. Simple Hash Function

Here’s a simple custom hash function for learning purposes:

  function simpleHash(str) {
    let hash = 0;
    for (let i = 0; i < str.length; i++) {
      const char = str.charCodeAt(i);
      hash = (hash << 5) - hash + char;
      hash |= 0; // Convert to 32bit integer
    }
    return hash;
  }
  console.log(simpleHash('hello world')); // Simple hash of the string 'hello world'

3. Using MurmurHash

MurmurHash is a popular non-cryptographic hash function:

  function murmurhash3_32_gc(key, seed) {
    let remainder, bytes, h1, h1b, c1, c2, k1, i;
    remainder = key.length & 3; // key.length % 4
    bytes = key.length - remainder;
    h1 = seed;
    c1 = 0xcc9e2d51;
    c2 = 0x1b873593;
    i = 0;

    while (i < bytes) {
      k1 =
        (key.charCodeAt(i) & 0xff) |
        ((key.charCodeAt(++i) & 0xff) << 8) |
        ((key.charCodeAt(++i) & 0xff) << 16) |
        ((key.charCodeAt(++i) & 0xff) << 24);
      ++i;

      k1 = ((k1 & 0xffff) * c1 + ((((k1 >> 16) * c1) & 0xffff) << 16)) & 0xffffffff;
      k1 = (k1 << 15) | (k1 >> 17);
      k1 = ((k1 & 0xffff) * c2 + ((((k1 >> 16) * c2) & 0xffff) << 16)) & 0xffffffff;

      h1 ^= k1;
      h1 = (h1 << 13) | (h1 >> 19);
      h1b = ((h1 & 0xffff) * 5 + ((((h1 >> 16) * 5) & 0xffff) << 16)) & 0xffffffff;
      h1 = (h1b + 0x6b64e854 + (((h1b >> 16) + (h1b & 0xffff)) & 0xffff)) & 0xffffffff;
    }

    k1 = 0;
    switch (remainder) {
      case 3:
        k1 ^= (key.charCodeAt(i + 2) & 0xff) << 16;
      case 2:
        k1 ^= (key.charCodeAt(i + 1) & 0xff) << 8;
      case 1:
        k1 ^= (key.charCodeAt(i) & 0xff);
        k1 = ((k1 & 0xffff) * c1 + ((((k1 >> 16) * c1) & 0xffff) << 16)) & 0xffffffff;
        k1 = (k1 << 15) | (k1 >> 17);
        k1 = ((k1 & 0xffff) * c2 + ((((k1 >> 16) * c2) & 0xffff) << 16)) & 0xffffffff;
        h1 ^= k1;
    }

    h1 ^= key.length;
    h1 ^= h1 >> 16;
    h1 = ((h1 & 0xffff) * 0x85ebca6b + ((((h1 >> 16) * 0x85ebca6b) & 0xffff) << 16)) & 0xffffffff;
    h1 ^= h1 >> 13;
    h1 = ((h1 & 0xffff) * 0xc2b2ae35 + ((((h1 >> 16) * 0xc2b2ae35) & 0xffff) << 16)) & 0xffffffff;
    h1 ^= h1 >> 16;

    return h1 >>> 0;
  }

  console.log(murmurhash3_32_gc('hello world', 1)); // MurmurHash of the string 'hello world'

App Example Using Introduced APIs

Let's create a simple Node.js application to store and verify user passwords using hashing:

  const crypto = require('crypto');

  // Function to hash a string (password)
  function hashString(str) {
    return crypto.createHash('sha256').update(str).digest('hex');
  }

  // Register user with hashed password
  let users = [];
  function registerUser(username, password) {
    const hashedPassword = hashString(password);
    users.push({ username, password: hashedPassword });
    console.log(`User ${username} registered successfully!`);
  }

  // Verify user password
  function verifyUser(username, password) {
    const user = users.find(user => user.username === username);
    if (user && user.password === hashString(password)) {
      console.log('Password is correct!');
    } else {
      console.log('Password is incorrect!');
    }
  }

  // Demonstrate the usage
  registerUser('john_doe', '12345');
  verifyUser('john_doe', '12345');
  verifyUser('john_doe', 'wrongpassword');

In the example above, we used the crypto library to hash user passwords and verify them during login attempts.

Hash: bec26dca2ca64f141838ceb3db254cc424373c5ac3c9d60636cf1d63dcbd30c4