locutus/esm/tcl/string/range.js

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

const parseIndex = (input, length) => {
    if (typeof input === 'number') {
        return Math.trunc(input);
    }
    const token = String(input).trim();
    if (token === 'end') {
        return length - 1;
    }
    const endOffset = token.match(/^end-(\d+)$/);
    if (endOffset?.[1]) {
        return length - 1 - Number(endOffset[1]);
    }
    return Math.trunc(Number(token));
};
export function range(str, first, last) {
    //      discuss at: https://locutus.io/tcl/range/
    // parity verified: Tcl 8.6
    //     original by: Kevin van Zonneveld (https://kvz.io)
    //       example 1: range('Hello World', 0, 4)
    //       returns 1: 'Hello'
    //       example 2: range('Hello World', 6, 'end')
    //       returns 2: 'World'
    //       example 3: range('abcdef', 1, 'end-1')
    //       returns 3: 'bcde'
    const value = String(str);
    const len = value.length;
    let start = parseIndex(first, len);
    let end = parseIndex(last, len);
    if (!Number.isFinite(start)) {
        start = 0;
    }
    if (!Number.isFinite(end)) {
        end = -1;
    }
    start = Math.max(0, start);
    end = Math.min(len - 1, end);
    if (start > end || len === 0) {
        return '';
    }
    return value.slice(start, end + 1);
}