thi-ng/umbrella

/**
 * Iterator version of `String.prototype.split()`. Yields iterable of substrings
 * of `src`, delimited by given regexp (default: unix & windows linebreaks).
 *
 * @remarks
 * Use this function to avoid creating an entire full copy of the original
 * source string, e.g. when only single-token or line-based accesses are needed.
 * This function is ~2x faster for large strings (benchmarked with 8MB & 16MB
 * inputs), with dramatically lower memory consumption.
 *
 * If given an regexp as `delim`, the function ensures the regexp has its global
 * flag enabled.
 *
 * @param src -
 * @param delim -
 * @param includeDelim -
 */
export function* split(
    src: string,
    delim: RegExp | string = /\r?\n/g,
    includeDelim = false
) {
    let i = 0;
    const n = src.length;
    const include = ~~includeDelim;
    let re: RegExp;
    if (typeof delim === "string") {
        re = new RegExp(delim, "g");
    } else if (!delim.flags.includes("g")) {
        re = new RegExp(delim, delim.flags + "g");
    } else {
        re = delim;
    }
    for (; i < n; ) {
        const m = re.exec(src);
        if (!m) {
            yield src.substring(i);
            return;
        }
        const len = m[0].length;
        yield src.substring(i, m.index + include * len);
        i = m.index + len;
    }
}