indexed-string-variation/dist/index.js

Experimental JavaScript module to generate all possible variations of strings over an alphabet using an n-ary virtual tree

export const defaultAlphabet = 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789';
function cleanAlphabet(alphabet) {
    return Array.from(new Set(alphabet.split(''))).join('');
}
// calculates the level of a given index in the current virtual tree
const getLevel = (base, index) => {
    let level = 0n;
    let current = index;
    let parent;
    while (current > 0n) {
        parent = (current - 1n) / base;
        level++;
        current = parent;
    }
    return level;
};
// Generates a string based on the given index and alphabet
function generateString(startIndex, alphabet) {
    if (startIndex === 0n)
        return '';
    const n = BigInt(alphabet.length);
    let result = '';
    let l;
    let f;
    let rebasedPos;
    let rebasedIndex;
    let index = startIndex;
    while (index > 0n) {
        l = getLevel(n, index);
        f = 0n;
        for (let i = 0n; i < l; i++) {
            f += n ** i;
        }
        rebasedPos = index - f;
        rebasedIndex = ((rebasedPos % n) + n) % n; // ensure non-negative
        result = alphabet[Number(rebasedIndex)] + result;
        index = (index - 1n) / n;
    }
    return result;
}
export function* indexedStringVariation(options = {}) {
    const alphabet = options.alphabet
        ? cleanAlphabet(options.alphabet)
        : defaultAlphabet;
    const from = options.from ?? 0n;
    let iterations = 0;
    let i = from;
    while (true) {
        const str = generateString(i, alphabet);
        if (options.maxLen !== undefined && str.length > options.maxLen) {
            break;
        }
        yield str;
        i++;
        iterations++;
        if (options.to !== undefined && i > options.to) {
            break;
        }
        if (options.maxIterations !== undefined &&
            iterations >= options.maxIterations) {
            break;
        }
    }
}
export default indexedStringVariation;