We don't need null

Nullish values, a small introduction

While many programming languages that have a “nullish” type (null, nil, etc.) debate about avoiding it, JavaScript is the only popular one with two; that’s right, two nullish types. Therefore, one of the most common recommendations is to use only one, and my recommendation is only to use undefined and avoid null. This article will explain why we might want to avoid null in JavaScript and TypeScript.

Why is it so common to avoid nullish values?

The creator of null pointers (Tony Hoare) is known for calling his creation a “billion-dollar mistake”:

I call it my billion-dollar mistake (…) My goal was to ensure that all use of references should be absolutely safe, with checking performed automatically by the compiler. But I couldn’t resist the temptation to put in a null reference, simply because it was so easy to implement. This has led to innumerable errors, vulnerabilities, and system crashes, which have probably caused a billion dollars of pain and damage in the last forty years.

When we use nullish values, we want to express that something is “not there,” a “no-value.” Generally, in typed languages, we represent those as “optional values” because they can either be set or be nullish.

The direct implication is that we need to test every “optional value” for its type and the nullish value it can take.

Now, imagine how bad it is for a language to have two nullish values. We now need to test for not two different types but three. This negatively affects maintenance, readability, and overall code quality. Because of this is that the most common recommendation is to avoid nullish as much as possible, and in JavaScript, try to stick to using only one. In the following sections, we will discuss why I (and many other developers) prefer undefined over null.

The nullish that the language uses

As Douglas Crockford (the father of JSON) put it in one of his talks, JavaScript itself uses undefined all the time, so let’s use the one the language uses:

let something; // This is undefined!

const otherThing = {
	foo: "hi",
};
otherThing.bar; // This is also undefined

const aFunction = anArgument => {
	// anArgument here is undefined if no value is passed
};

To use null in all those scenarios, we need to explicitly set the values to null, which will look like this:

let something = null;

const otherThing = {
	foo: "hi",
	bar: null,
};

const aFunction = (anArgument = null) => {};

For me, that sounds like undefined with extra steps.

What if I want to define a nullish value intentionally?

In that case, assign undefined to it:

const anObject = {
	...otherObject,
	propertyToNullify: undefined,
};

That nasty bug with the type of null

We all know at this point about the bug with typeof null; that bug doesn’t apply to undefined, which works as expected:

typeof null; // "object" 🤷🏻
typeof undefined; // "undefined" 🎉

Why would we use a bugged value intentionally? This is well known, but just in case here’s a backup of Mozilla’s JS API, you can read trough that code to see how typeof null is implemented, and why it’s bugged, but long story short it was a mistake with bitwise operators. There was a proposal to fix it, but was discarded.

Smaller API responses

Response bodies are drastically smaller if we rely on undefined instead of null. Here’s a response example using null:

{
	"foo": "foo",
	"bar": null
}

Compared with undefined:

{
	"foo": "foo"
}

If you care at least a little about carbon emissions, you should care about the size of your responses.

The case with Array

Array is a particular case because when we create a new array of a given size, the items inside said array are empty, not undefined. This empty means that if we check for their value, it will give us undefined, but they aren’t taking any space in memory (performance reasons), so if we try to loop over it, it will provide us with nothing:

const array = new Array(3); // [empty, empty, empty]
array[0] === undefined; // true
array.map(console.log); // nothing logs 🤦🏻

The arguments in favor of null

When I say that we don’t need null, folks that use it a lot (generally coming from other languages with null as the only nullish value) get pretty mad about such claims. The most common response I get is:

null is for intentional missing values, and undefined should be used when the values were never set in the first place.

The first thing I think with responses like that is: Why would we ever need to make that distinction? Both are “nullish,” and we don’t need to differentiate between “intentionally missing” and “unintentionally missing.” One common usage of null is to do stuff like this:

const people = [
	{
		firstName: "Lou",
		middleName: null,
		lastName: "Cyx",
	},
	{
		firstName: "Barack",
		middleName: "Hussein",
		lastName: "Obama",
	},
];

But we can omit middleName when the user doesn’t have one:

const people = [
	{
		firstName: "Lou",
		lastName: "Cyx",
	},
	// ...
];

And we can set middleName to an empty string if the user intentionally left that blank if we need to know that for some reason:

const people = [
	{
		firstName: "Lou",
		middleName: "",
		lastName: "Cyx",
	},
	// ...
];

And the TypeScript representation would be something like this:

type Person = {
	firstName: string;
	middleName?: string;
	lastName: string;
};

So why would we waste memory with a null value or bits with a JSON response when we can omit what is not there?

But the API is responding with null (maybe written in Java), so I have to use null all over my app as well.

My answer to that is: We should use an API wrapper. Instead of “spreading” null all over our codebase, we should update our surface of contact with the API, so nulls are turned into undefineds. If we have any contact with the folks making the API, we should voice our concern about making API responses smaller by eliminating null values.

But in React I use null when I want a component to not render anything

We can use undefined as well.

We have to type 5 more characters when we write undefined explicitly in our code.

Generally, we will rely on it implicitly (omitting the value), but even if we had to type it every time, it is worth it compared to all the downsides of null.

Languages without nullish

There are languages out there that don’t have nullish values and instead rely on Maybe, which is a type that means “we might get a certain type or nothing.” We can do a simple implementation of that in TypeScript like this:

type Maybe<Type> = Type | undefined;

So we might get whatever type we are expecting or undefined. We can just use ? as well when it’s a property or argument:

const aFunction = (optionalArgument?: Type) => {
	/* Function content */
};

type AnObject = {
	optionalProperty?: Type;
};

To deal with our “Maybes,” we can use operators such as nullish coalescing (??) and optional chaining (?.), so…

// We don't need to do something nasty like this:
const greet = name => `Hello, ${name !== null ? name : "Guest"}`;

// We can do this:
const greet = name => `Hello, ${name ?? "Guest"}`;

// Or better yet, because we are using undefined, we can actually...
const greet = (name = "Guest") => `Hello, ${name}`;

Linting like a champ

We can enforce avoiding null by using this great ESLint plugin, and adding this to our linting rules:

import eslintPluginNoNull from "eslint-plugin-no-null";

export default [
	{
		plugins: { "no-null": eslintPluginNoNull },
		rules: { "no-null/no-null": "error" },
	},
];

Other sources

Here’s a list of some sources by other developers that share my opinion about null:

• Abandon null in favor of undefined in Angular.
• Null is bad by a lot of people.
• Why you should always use undefined, and never null by Fredrik Söderström.
• TypeScript coding guidelines
• A StackOverflow answer.
• The Better Parts by Douglas Crockford.

Closing thoughts

My opinion about null in JavaScript is that “anything written with null can and should be written with undefined instead.” So, as usual, I close this article with a few open questions: Do we NEED to use null? Don’t we have a way of resolving “that” issue without it?