# How to Remove All Falsy Values from an Array in JavaScript

This is one of my favorite algorithm challenge! Because it covers a fundamental topic of JavaScript. And how that knowledge is used to solve this problem. Let's go!

• falsy values
• boolean !!
• filter

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# The Challenge

Write a function that returns an array of only truthy values

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# 1. Falsy values

Falsy values is absolutely a must know for JavaScript developers. When I first started learning JS, I made the mistake of trying to memorizing what was "truthy". It always confused me. Did you know an empty array is a truthy value, that always threw me off 🤦‍♀️. Instead, just focus on learning the falsy values. And whatever is NOT on that falsy list, then it's considered truthy 👍

Here's a list of all the falsy values

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# 2. !!

Once you know the falsy values, we can call !! to convert a value to a Boolean. But you can also use Boolean(value) to do the conversion too.

Coerce value to a Boolean value

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# 3. filter()

Next, we want to remove all the falsy value from our array. In other words, we want to "filter" out the falsy values and just keep the truthy values.

Create a new array with only truthy values

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# Final Solution

Woohoo! You conquered another algorithm challenge! You have successfully solved how to remove all falsy values from an array 👏

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# More Solutions

Using !!

function removeFalsy(arr) {
  return arr.filter(a => !!a);
}

Using Boolean

function removeFalsy2(arr) {
  return arr.filter(a => Boolean(a));
}

Using Boolean directly

function removeFalsy3(arr) {
  return arr.filter(Boolean);
}

This works because Boolean itself is a function, and the arguments filter supplies are passed directly to it. This is the same as:

function removeFalsy3(arr) {
  return arr.filter(a => Boolean(a));
}

Boolean() is also a function that returns truthy when true and falsy when false!

var a = [1, 2, 'b', 0, {}, '', NaN, 3, undefined, null, 5];

var b = a.filter(Boolean); // [1, 2, "b", {}, 3, 5];

Using Filter's Auto Coercion

function removeFalsy3(arr) {
  return arr.filter(a => a);
}