filter()

The filter() method creates a new array with all elements that pass the test implemented by the provided function.

var words = ["spray", "limit", "elite", "exuberant", "destruction", "present"];

var longWords = words.filter(word => word.length > 6);

// Filtered array longWords is ["exuberant", "destruction", "present"]

Syntax

var newArray = arr.filter(callback[, thisArg])

Filtering out all small values

const isBigEnough = (value) => value >= 10;

var filtered = [12, 5, 8, 130, 44].filter(isBigEnough);
// filtered is [12, 130, 44]

Filtering invalid entries from JSON

var arr = [
  { id: 15 },
  { id: -1 },
  { id: 0 },
  { id: 3 },
  { id: 12.2 },
  { },
  { id: null },
  { id: NaN },
  { id: 'undefined' }
];

var invalidEntries = 0;

function isNumber(obj) {
  return obj!== undefined && typeof(obj) === 'number' && !isNaN(obj);
}

function filterByID(item) {
  if (isNumber(item.id)) {
    return true;
  } 
  invalidEntries++;
  return false; 
}

var arrByID = arr.filter(filterByID);

console.log('Filtered Array\n', arrByID); 
// Filtered Array
// [{ id: 15 }, { id: -1 }, { id: 0 }, { id: 3 }, { id: 12.2 }]

console.log('Number of Invalid Entries = ', invalidEntries); 
// Number of Invalid Entries = 4

Searching in array

const fruits = ['apple', 'banana', 'grapes', 'mango', 'orange'];

/**
 * Array filters items based on search criteria (query)
 */
const filterItems = (query) => {
  return fruits.filter((el) =>
    el.toLowerCase().indexOf(query.toLowerCase()) > -1
  );
}

console.log(filterItems('ap')); // ['apple', 'grapes']
console.log(filterItems('an')); // ['banana', 'mango', 'orange']