locutus/lua/string/sub.js

Locutus other languages' standard libraries to JavaScript for fun and educational purposes

"use strict";
Object.defineProperty(exports, "__esModule", { value: true });
exports.sub = sub;
function sub(s, i, j) {
    //      discuss at: https://locutus.io/lua/sub/
    // parity verified: Lua 5.4
    //     original by: Kevin van Zonneveld (https://kvz.io)
    //          note 1: Lua uses 1-based indexing, negative indices count from end
    //       example 1: sub('Hello', 1, 3)
    //       returns 1: 'Hel'
    //       example 2: sub('Hello', 2)
    //       returns 2: 'ello'
    //       example 3: sub('Hello', -2)
    //       returns 3: 'lo'
    s = String(s);
    const len = s.length;
    // Convert Lua 1-based index to JS 0-based
    // Negative indices count from end in Lua
    let start = i < 0 ? len + i : i - 1;
    let end = j === undefined ? len : j < 0 ? len + j + 1 : j;
    // Clamp to valid range
    if (start < 0) {
        start = 0;
    }
    if (end > len) {
        end = len;
    }
    if (start >= end) {
        return '';
    }
    return s.substring(start, end);
}