__slice.js

__slice = function __slice(source, start, end, step) {
  var length, result, stringify;
  if (!(typeof source !== "undefined" && source !== null)) {
    throw "'source' cannot be empty when calling __slice(>> " + source + " <<, " + start + ", " + end + ", " + step + ")";
  } else if (step === 0) {
    throw "'step' cannot be zero when calling __slice(..., " + start + ", " + end + ", >> " + step + " <<)";
  }
  if (Object.prototype.toString.call(source) !== "[object Array]") {
    source = source.toString().split("");
    stringify = true;
  }
  length = source.length;
  start = (typeof start !== "undefined" && start !== null) ? (start < 0 ? start + length : start) : 0;
  start < 0 ? (start = 0) : null;
  end = (typeof end !== "undefined" && end !== null) ? (end < 0 ? end + length : end) : length;
  end < 0 ? (end = start) : end > length ? (end = length) : null;
  if (start === end) {
    result = [];
  } else {
    step = (typeof step !== "undefined" && step !== null) ? step : (start <= end ? 1 : -1);
    if (step === 1) {
      result = Array.prototype.slice.call(source, start, end);
    } else if (step === -1) {
      result = Array.prototype.reverse.call(Array.prototype.slice.call(source, start, end));
    } else {
      result = [];
      while (step > 0 ? start < end : start > end) {
        result.push(source[start]);
        start = start + step;
      }
    }
  }
  return (stringify ? result.join("") : result);
};

console.log(__slice("hello, world", 3, 5)); // 'lo'
console.log(__slice("hello, world", 10)); // 'ld'
console.log(__slice("hello, world", null, null, -1)); // 'dlrow ,olleh'
console.log(__slice("hello, world", -11, -7, -1)); // 'olle'