everyutil/string/stringEntropy.js

A comprehensive library of lightweight, reusable utility functions for JavaScript and TypeScript, designed to streamline common programming tasks such as string manipulation, array processing, date handling, and more.

"use strict";
Object.defineProperty(exports, "__esModule", { value: true });
exports.stringEntropy = void 0;
/**
 * Returns the Shannon entropy of a string.
 *
 * Useful for detecting randomness, passwords, or encoded data.
 *
 * @author @dailker
 * @param {string} str - The input string.
 * @returns {number} The Shannon entropy.
 */
function stringEntropy(str) {
    const freq = new Map();
    for (const ch of str)
        freq.set(ch, (freq.get(ch) ?? 0) + 1);
    const n = str.length;
    let ent = 0;
    for (const count of freq.values()) {
        const p = count / n;
        ent -= p * Math.log2(p);
    }
    return ent;
}
exports.stringEntropy = stringEntropy;