array.filter()

Overview

Similar to array.map(), the array.filter() function iterates over an array and runs a callback for each element. The callback receives the value and the index of the array element as a parameter.

.filter() will always return you a new array, comprised of elements from the original array that match your criteria – which elements in the array match the filter condition?

Even Numbers

  let numbers = [2,3,4,5];
  
  let evens = numbers.filter( function(n,i) {
    return !(n % 2);
  });
  
  // or as a snazzy arrow function ...
  // let evens = numbers.filter( n => !(n % 2) );
  
  console.log(evens); // [ 2, 4, 6 ]

Object Values

  let people = [
    { name: 'John', role: 'Dad' },
    { name: 'Cathy', role: 'Mom' },
    { name: 'Zach', role: 'Kid' },
    { name: 'Allie', role: 'Kid' },
  ];

  let parents = people.filter(person => person.role !== "Kid");
  console.log(parents);
   // [ { name:'John' ... }, {name:'Cathy', ...} ]

If you do nothing … you’ll get back an empty array

  let numbers = [2,3,4,5];
  
  let evens = numbers.filter( function(n,i) {
  });
  
  console.log(evens); // []

Caveats and Notes

Reference