How to Filter for True Values in an Array in JavaScript

Ferenc Almasi • 🔄 2021 April 26 • 📖 2 min read

Probably one of the simplest and cleanest ways to get rid of falsy values in JavaScript is by utilizing the built-in filter array function the following way:

// Filter out falsy values by simply passing Boolean to Array.prototype.filter
[
  1, 2, 3, 0, 
  undefined, 
  null, 
  false, 
  true, 
  '', 
  'I’m truthy 🙂'
].filter(Boolean);

// Results in the following array:
[1, 2, 3, true, 'I’m truthy 🙂'];

filter.js

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The only problem is that this won't work for nested arrays. To get around this, you can use the below function which uses recursion to filter out falsy values from a nested array:

const filterFalsy = array => array.filter(Boolean)
                                  .map(item => Array.isArray(item) ? filterFalsy(item) : item);

const array = [
  1, 2, 3, 0, 
  undefined, 
  null, 
  false, 
  true,
  [0, 1, 2, '', [false, true]], 
  '', 
  'I’m truthy 🙂'
];

filterFalsy(array); // This will return the following array:

[1, 2, 3, true, [1, 2, [true]], "I’m truthy 🙂"]