node-vitals/test/helpers/slice-arr.js

Do more with less. A simple, high-performing, functional JavaScript library.

/**
 * -----------------------------------------------------------------------------
 * VITALS UNIT TESTS HELPER: sliceArr
 * -----------------------------------------------------------------------------
 * @author Adam Smith <adam@imaginate.life> (https://github.com/imaginate)
 * @copyright 2017 Adam A Smith <adam@imaginate.life> (https://github.com/imaginate)
 *
 * Annotations:
 * @see [JSDoc3](http://usejsdoc.org)
 * @see [Closure Compiler JSDoc Syntax](https://developers.google.com/closure/compiler/docs/js-for-compiler)
 */

'use strict';

module.exports = sliceArr;

/**
 * @param {(!Object|function)} source
 * @param {number=} start - [default= 0]
 * @param {number=} end - [default= source.length]
 * @return {!Array}
 */
function sliceArr(source, start, end) {

  /** @type {!Array} */
  var arr;
  /** @type {number} */
  var len;
  /** @type {number} */
  var ii;
  /** @type {number} */
  var i;

  len = source.length;
  start = start
    ? start < 0
      ? len + start
      : start
    : 0;
  start = start < 0 ? 0 : start;
  end = end === undefined || end > len
    ? len
    : end < 0
      ? len + end
      : end;

  if (start >= end) return [];

  arr = new Array(end - start);
  ii = start - 1;
  i = 0;
  while (++ii < end) {
    arr[i++] = source[ii];
  }
  return arr;
}