Array Methods in JavaScript: Filter, Map, Reduce

array-methods-in-javascript-filter-map-reduce.js

var data = ['apple', 'pear', 'orange', 'orange', 'apple', 'lime', 'lime'];

data
  .filter((item, index, array) => item !== 'pear') /* Let's filter out all pears (as they are horrible!) */
  .reduce((total, item, index, array) => {
    if (total.indexOf(item) === -1) total.push(item); // Only add unique items to the array (de-duplication)
    return total; // Return the cumulative total
  }, [] /* Initial value, can be any primitive e.g. [], boolean etc */)
  .map((item, index, array) => item + ' juice') /* Add the word 'juice' to the end */
  .forEach((item, index, array) => item + ' ' + index) /* Add an index */
  .reduce((total, item, index, array) => {
    index !== array.length - 1 ? total += item + ' and ' : total += item; // Concat into one string and add 'and', unless its the last element
    return total; // Return the cumulative total
  }, '' /* Initial value, can be any primitive e.g. [], boolean etc */);
 
// Outputs: "apple juice and orange juice and lime juice"