Easy Ways to Check If an Array is Empty in JavaScript

🔥 Quickfire # Javascript

Pravin Prajapati · 03 May 2024

Check if an array is empty in JavaScript

Every developer must be aware of Java scripts, and working with arrays is the foundation of many web development tasks. These arrays could be generated by your website's server, from an external source such as an API, or by yourself. Checking if an array is empty is a common task in JavaScript, and several efficient ways exist.

Here is a simple way to truthfully check empty arrays in javascript. In this short guide, we'll cover four simple methods for checking if an array is empty.

Applying the length property with the === operator

Applying the length property with the ! operator

Applying the Array.isArray() method

Gotcha: Applying the === [] syntax

1. Applying the length property with the === operator

To Check Empty Array in JavaScript, use the length property with the === operator. The length property indicates how many items exist in the array. If it's empty, the length will be 0, so you can check if the length is exactly 0 to see if the array is empty.

For example, if you have an empty array called names:

const names = [];
const isEmpty = names.length === 0; // true

// And if you have an array with some items:

const names = ['Ram', 'Rohan'];
const isEmpty = names.length === 0; // false

But there are some things to be careful about when using this method, and we'll discuss them later in this article.

2. Applying the length property with the ! operator

The second method to check if a JavaScript array is empty is using the length property with the! Operator. The! operator is the logical NOT operator. Since 0 is considered false in JavaScript, we can use ! to flip the truthiness of the length property.

If your array is empty, the length property will be 0 (which is false), so the expression will return true:

const names = [];
const isEmpty = !names.length; // true

// If your array is not empty, the length property will be an integer greater than 0 (which is true), so the expression will return false.

const names = ['Ram', 'Rohan'];
const isEmpty = !names.length; // false

As with the first method, there are some things to remember when using this approach, which we will review next.

3. Applying the Array.isArray() method

While using the length property can help check if a JavaScript array is empty, it must only sometimes be a reliable strategy since other JavaScript objects also have a length property. So, before we check the length of an array, we must first check that it is an array.

One option is to use the Array.isArray() method in conjunction with the length property check. This method checks whether a variable is an array, giving us more confidence in our code.

Here's how you can use it:

const names = [];
Array.isArray(names) && names.length === 0; // true

Using Array.isArray() helps ensure we deal with an array.

For example, if we have a JavaScript object like this:

const names = {
length: 0,
};

Checking its length directly would wrongly indicate it's empty.

names.length === 0; // true

But using Array.isArray() gives us a more accurate result:

Array.isArray(names) && names.length === 0; // false

Plus, Array.isArray() can filter out array-like objects such as NodeList.

const nodes = document.querySelectorAll('div');
Array.isArray(nodes) && nodes.length === 0; // false

So, while Array.isArray() does not directly reveal whether an array is empty.

It does confirm that we are working with an array, which boosts our confidence in our tests.

4. Gotcha: Applying the === [] syntax

When attempting to check if a JavaScript array is empty, a standard error is to use === [] as you would in PHP.

However, in JavaScript, this approach will always return false.

Using === [] to check if an array with items is empty will correctly return false.

const names = ['Ram', 'Rohan'];
names === []; // false

Even if you use === [] to check if an empty array is empty, the result is false:

const names = [];
names === []; // false

This is because arrays in JavaScript are objects. So, when you use === [], you compare their identities rather than their values.

For example:

const names = ['Ram', 'Rohan'];
names === names; // true

In this code, we are comparing the identity of the name array to itself.

Because it is the same array, it returns true.

However, when we try to compare it to another array with the same values,

const names = ['Ram', 'Rohan'];
names === ['Ram', 'Rohan']; // false

It returns false because they are different arrays despite having the same values.

Why Handling Empty Arrays Matters

Empty arrays are easily overlooked but handling them correctly is a point of insurance policy for productive web applications. What if a form with a submit button isn't activating because the code erroneously believes there's data in an empty array? These petty problems catch the users off balance which is a backward way to lead your application out of the estimated result.

The Role of Array.isArray()

JavaScript comes with an Array.isArray() method that helps you easily determine if a variable is an array. Therefore, the variable doesn't have to be confused with null, undefined, or other types which are not arrays. This will guarantee you that your code functions with the desired effect.

Why Not Just Check the Length Property?

If you are wondering about the possibility of not using the length property only to check if an array is empty, then your thinking is justified. The problem is that other data types, such as strings, also have a length property, which can result in you presuming an array.

Example: length Property with Strings

const string = 'Hello World';
console.log(string.length); // Output: 11
console.log(Array.isArray(string)); // Output: false

In this example, the length property for a string tells us the number of characters, whereas Array.isArray() confirms it’s not an array.

Why This Matters

Shared Property, Different Meanings: Both strings and arrays have a length property by their nature, but you may use it for different purposes. In strings, length equals characters, and in arrays, it counts elements (even empty slots in case of sparse arrays).
Know Your Data Type: The length property tells you how many items you have — whether you are using a string, an array, or an array-like object (NodeList or arguments object) will affect how you use it. For example, if you are dealing with a collection of elements, it will be very important to know if the elements in your collection are actually an array or some other structure. This knowledge will have an effect on the way you will iterate and convert it in case it is needed.
More Than Just Length: This underpins a fundamental point in JavaScript: knowing the type and shape of your data alongside knowing the properties and methods at your disposal is equally as important. The length property is handy, yet what you choose to do with it is determined by whether your string, array, or array-like object.

We also write a blog for Check If an Array Is Empty in PHP. You can also learn many development-related gigs from our blog page.

Also Read: 4 Easy Ways to Check If an Array Is Empty in PHP

Understanding the Proper Way to Check if an Array is Empty in JavaScript (and Avoiding Unconventional Methods)

JavaScript offers a variety of methods to check if an array is empty, with the simplest and most practical approach being the use of the length property. For example:

const isEmpty = array => array.length === 0;

This approach is clear, concise, and widely understood by developers. However, JavaScript's flexibility allows for some unconventional or unnecessarily complex methods to achieve the same goal. While these methods may showcase creativity or exploit certain quirks of the language, they are not recommended for real-world projects due to their inefficiency, lack of clarity, or potential for introducing errors.

Here are some examples of unconventional methods to check if an array is empty, along with reasons why they should be avoided:

1. Using JSON.stringify

const isEmpty = array => JSON.stringify(array) === '[]';

Here, the array is converted to a JSON string and compared to '[]'. While this works, it introduces unnecessary computational overhead and is far less clear than simply using .length.

2. Combining map and reduce

const isEmpty = array => array.map(() => 1).reduce((a, b) => a + b, 0) === 0;

This convoluted method sums the "mapped" values of an array to determine if it’s empty. While it might appeal to those exploring functional programming, it’s impractical.

3. Using the Spread Operator with Math Functions

const isEmpty = array => Math.max(...array) === -Infinity;

Since Math.max returns -Infinity when given no arguments, this method exploits that behavior to check for an empty array. It’s clever but far from intuitive.

4. Using Logical NOT with length

const isEmpty = array => !!array.length === false;

Double negating the length property transforms it into a boolean and then negates it to check for emptiness. This works but is unnecessarily verbose compared to array.length === 0.

5. Checking Undefined Values

const isEmpty = array => array[0] === undefined && array.length === 0;

This method redundantly checks both the first element and the length, complicating what should be a straightforward operation.

6. Using join

const isEmpty = array => array.join(',') === '';

By converting the array to a string and comparing the result to an empty string, this method works but lacks efficiency and clarity.

7. Employing filter

const isEmpty = array => array.filter(() => false).length === 0;

This filters out all elements with a condition that always evaluates to false. While creative, it’s over-engineered and less efficient.

8. Serializing and Parsing

const isEmpty = array => JSON.parse(JSON.stringify(array)).length === 0;

This unnecessarily converts the array to JSON and back, adding computational cost and reducing code readability.

9. Using toString

const isEmpty = array => array.toString() === '';

When an array’s toString method is called, it returns a comma-separated string of its elements. An empty array results in an empty string, but relying on this method is indirect and not intuitive.

10. Custom Reducers

const isEmpty = array => array.reduce((acc, curr) => acc + 1, 0) === 0;

This approach sums up the elements using reduce. While technically correct, it’s overly complicated for such a simple check.

11. Using every

const isEmpty = array => array.every(() => false);

Here, the every method tests if all elements match a condition (which always evaluates to false). For an empty array, this condition is satisfied by default, making this a quirky but confusing solution.

12. Function Invocation with Spread Syntax

const isEmpty = array => ((...args) => args.length === 0)(...array);

This method spreads the array into a function’s arguments and checks the argument count. While creative, it’s not practical.

13. Using findIndex

const isEmpty = array => array.findIndex(() => true) === -1;

The findIndex method returns -1 when no element matches the given condition. For an empty array, this will always happen, making it another roundabout approach.

14. Checking pop Behavior

const isEmpty = array => {
  const copy = [...array];
  return copy.pop() === undefined && copy.length === 0;
};

This method checks if popping an element returns undefined and verifies the length afterward. It’s inefficient and unnecessary.

15. Using forEach

const isEmpty = array => {
  let hasElements = false;
  array.forEach(() => hasElements = true);
  return !hasElements;
};

This manually iterates over the array and sets a flag if elements are present. While it works, it’s verbose and not ideal.

Always aim for clarity and simplicity in your code. The direct and conventional approach of using array.length === 0 is not only easier to read and maintain but also performs better than the unconventional alternatives. While exploring creative methods can be fun for learning, avoid using them in production code to maintain professional standards and avoid confusion.

Essence

These methods can help you Check Empty Array in JavaScript. We prepared this guide for developers who need help with the common issue of finding an empty array in JavaScript. Elightwalk Technology offers a variety of solutions for developers and businesses to learn, update, and create new websites using leading solution formulas. Contact us if you have any technological questions or need guidance on developing related solutions. Our development team assists you and guides you to the right solution for your projects.

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Pravin Prajapati

Full Stack Developer

Expert in frontend and backend development, combining creativity with sharp technical knowledge. Passionate about keeping up with industry trends, he implements cutting-edge technologies, showcasing strong problem-solving skills and attention to detail in crafting innovative solutions.

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