array.js

/**
 * Returns an index of the specified element in array or -1 if element is not found
 *
 * @param {array} arr
 * @param {any} value
 * @return {number}
 *
 * @example
 *    ['Ace', 10, true], 10    => 1
 *    ['Array', 'Number', 'string'], 'Date'    => -1
 *    [0, 1, 2, 3, 4, 5], 5    => 5
 */

function findElement(arr, value) {
	for (let i = 0; i < arr.length; i++) {
	  if (arr[i] === value) {
		return i;
	  }
	}
	return -1;
  }

/**
 * Returns the doubled array - elements of the specified array are repeated twice
 * using original order
 *
 * @param {array} arr
 * @return {array}
 *
 * @example
 *    ['Ace', 10, true]  => ['Ace', 10, true,   'Ace', 10, true]
 *    [0, 1, 2, 3, 4, 5] => [0, 1, 2, 3, 4, 5,   0, 1, 2, 3, 4, 5]
 *    [] => []
 */

function doubleArray(arr) {
	return arr.concat(arr);
  }

/**
 * Returns an array of positive numbers from the specified array in original order
 *
 * @param {array} arr
 * @return {array}
 *
 * @example
 *    [ 0, 1, 2, 3, 4, 5 ] => [ 1, 2, 3, 4, 5 ]
 *    [-1, 2, -5, -4, 0] => [ 2 ]
 *    [] => []
 */

function getArrayOfPositives(arr) {
	return arr.filter(num => num > 0);
  }

/**
 * Removes falsy values from the specified array
 * Falsy values: false, null, 0, "", undefined, and NaN.
 * (https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Boolean#Description)
 *
 * @param {array} arr
 * @return {array}
 *
 * @example
 *    [ 0, false, 'cat', NaN, true, '' ] => [ 'cat', true ]
 *    [ 1, 2, 3, 4, 5, 'false' ]         => [ 1, 2, 3, 4, 5, 'false' ]
 *    [ false, 0, NaN, '', undefined ]   => [ ]
 */

function removeFalsyValues(arr) {
	return arr.filter(item => !!item);
  }

/**
 * Returns the array of string lengths from the specified string array.
 *
 * @param {array} arr
 * @return {array}
 *
 * @example
 *    [ '', 'a', 'bc', 'def', 'ghij' ]  => [ 0, 1, 2, 3, 4 ]
 *    [ 'angular', 'react', 'ember' ] => [ 7, 5, 5 ]
 */

function getStringsLength(arr) {
	return arr.map(str => str.length);
  }

/**
 * Returns the sum of all items in the specified array of numbers
 *
 * @param {array} arr
 * @return {number}
 *
 * @example
 *   [] => 0
 *   [ 1, 2, 3 ]           => 6
 *   [ -1, 1, -1, 1 ]      => 0
 *   [ 1, 10, 100, 1000 ]  => 1111
 */

function getItemsSum(arr) {
	return arr.reduce((sum, num) => sum + num, 0);
  }

module.exports = {
	findElement,
	doubleArray,
	getArrayOfPositives,
	removeFalsyValues,
	getStringsLength,
	getItemsSum,
};