locutus/esm/perl/core/rindex.js

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

export function rindex(str, substr, position) {
    //      discuss at: https://locutus.io/perl/rindex/
    // parity verified: Perl 5.40
    //     original by: Kevin van Zonneveld (https://kvz.io)
    //          note 1: Returns the last index of substr in str, or -1 when not found.
    //       example 1: rindex('hello hello', 'lo')
    //       returns 1: 9
    //       example 2: rindex('hello hello', 'lo', 8)
    //       returns 2: 3
    //       example 3: rindex('hello', 'x')
    //       returns 3: -1
    const source = String(str);
    const needle = String(substr);
    if (position === undefined) {
        return source.lastIndexOf(needle);
    }
    const from = Math.trunc(Number(position));
    if (!Number.isFinite(from)) {
        return source.lastIndexOf(needle);
    }
    return source.lastIndexOf(needle, from);
}