JavaScript Not Null Check: Best Practices

Aug 6, 2023

Categories:

javascript

nullcheck

bestpractices

Introduction

Performing a not null check in JavaScript is crucial for ensuring that variables are assigned valid values and avoiding unexpected errors in our code. Null or undefined values can cause various issues, such as crashing the application or producing incorrect results.

In JavaScript, null represents the intentional absence of any object value, while undefined indicates that a variable has been declared but has not been assigned a value. Both null and undefined can be problematic if not properly handled, as they can lead to runtime errors when trying to access properties or call methods on them.

It is important to be aware of different scenarios where null or undefined values can occur, such as when receiving data from external sources, when accessing elements in an array or object, or when passing arguments to functions. By performing not null checks, we can validate the values and handle these scenarios gracefully, improving the reliability and stability of our JavaScript code.

Checking for null or undefined

In JavaScript, there are different ways to check for null or undefined values. Here are some best practices:

Using strict equality (===) to check for null or undefined:
- The strict equality operator (===) checks for both value and type equality. It returns true if the value on the left is strictly equal to the value on the right, and false otherwise.
- To check if a variable is null or undefined, you can use the strict equality operator like this:
```
if (variable === null || variable === undefined) {
  // Handle null or undefined case
}
```
Utilizing the typeof operator to perform the check:
- The typeof operator returns a string indicating the type of the operand.
- To check if a variable is null or undefined using the typeof operator, you can do the following:
```
if (typeof variable === "object" && variable === null) {
  // Handle null case
}
if (typeof variable === "undefined") {
  // Handle undefined case
}
```
The use of the nullish coalescing operator (??) for concise null checks:
- The nullish coalescing operator (??) is a newer addition to JavaScript and provides a concise way to handle null or undefined values.
- It returns the value on the left if it is not null or undefined, otherwise, it returns the value on the right.
- Here's an example of using the nullish coalescing operator:
```
const result = variable ?? defaultValue;
```
Custom null check functions and their benefits:
- In some cases, you may need to perform more complex null checks or handle specific scenarios.
- Creating custom null check functions can help encapsulate the logic and improve code readability.
- Here's an example of a custom null check function:
```
function isNullOrUndefined(value) {
  return value === null || value === undefined;
}
if (isNullOrUndefined(variable)) {
  // Handle null or undefined case
}
```

These techniques provide different approaches to checking for null or undefined values in JavaScript. Choose the one that best suits your needs and the context of your code.

Diving into the best practices

When it comes to performing null checks in JavaScript, there are several best practices to follow. These practices can help improve code reliability and prevent errors caused by null or undefined values.

1. Early return technique

One effective technique for handling null or undefined values is the early return approach. This involves checking for null or undefined at the beginning of a function or block of code, and immediately returning or exiting the function if a null value is encountered.

By employing the early return technique, we can avoid unnecessary computations or operations on null values, reducing the likelihood of errors.

Here's an example of implementing the early return technique:

function calculateSum(array) {
  if (!Array.isArray(array)) {
    return 0;
  }

  let sum = 0;
  for (let i = 0; i < array.length; i++) {
    if (typeof array[i] !== 'number') {
      return 0;
    }
    sum += array[i];
  }

  return sum;
}

In the above example, we check if the input array is not an array using Array.isArray(array). If it's not an array, we return 0 immediately. This early return avoids any potential errors that could occur if we attempted to iterate over a non-array.

2. Optional chaining

Another best practice for null checks in JavaScript is to use optional chaining. Optional chaining simplifies null checks by allowing us to access properties or call methods on an object without explicitly checking for null or undefined beforehand.

Here's an example of using optional chaining:

const user = {
  name: 'John',
  address: {
    street: '123 Main St',
    city: 'Exampleville',
    country: 'USA'
  }
};

const country = user.address?.country;

In the above example, user.address?.country attempts to access the country property of the address object. If address is null or undefined, the expression will short-circuit and evaluate to undefined, preventing any potential errors.

3. Default values

Providing default values is another best practice when dealing with null or undefined values. By setting default values, we can ensure that our code continues to function properly even if a variable is null or undefined.

Here's an example of setting a default value:

function greetUser(name) {
  name = name || 'Guest';
  console.log(`Hello, ${name}!`);
}

greetUser(); // Output: Hello, Guest!
greetUser('John'); // Output: Hello, John!

In the above example, if the name argument is null or undefined, we set it to the default value of 'Guest' using the logical OR operator (||). This ensures that the greetUser function always has a valid name to work with.

By following these best practices, we can enhance the robustness and reliability of our JavaScript code when dealing with null or undefined values.

Continue to Conclusion

1. Early return technique

The early return technique is a best practice for handling null or undefined values in JavaScript. Instead of writing lengthy if-else statements to check for null or undefined values, the early return technique allows developers to exit a function early if a null or undefined value is encountered.

By using early returns, developers can improve code readability and reduce the complexity of their logic. This technique also helps prevent unnecessary code execution, as the function stops processing once a null or undefined value is encountered.

Here's an example of implementing the early return technique in different contexts:

// Example 1: Early return in a function
function calculateTotalPrice(quantity, price) {
  if (quantity === null || quantity === undefined || price === null || price === undefined) {
    return; // Exit the function early if any value is null or undefined
  }

  return quantity * price;
}

// Example 2: Early return in an event handler
function handleClick(event) {
  const target = event.target;
  
  if (target === null || target === undefined) {
    return; // Exit the event handler if the target element is null or undefined
  }
  
  // Continue with event handling logic
}

In both examples, the early return technique is used to check if a value is null or undefined. If any of the values are null or undefined, the function or event handler exits early without further processing.

Using the early return technique not only simplifies the code but also helps avoid potential errors that could occur when trying to perform operations on null or undefined values.

2. Optional chaining

Optional chaining is a feature introduced in JavaScript ES2020 that simplifies null checks by allowing us to safely access nested properties or methods of an object without causing an error if any of the intermediate properties or the object itself is null or undefined.

Before the introduction of optional chaining, we would have to perform multiple null checks to ensure that each property or method we access is not null or undefined. This could lead to verbose and repetitive code.

With optional chaining, we can simply use the question mark (?.) operator to safely access nested properties or methods. If any of the intermediate properties or the object itself is null or undefined, the expression evaluates to undefined instead of throwing an error.

Here's an example that demonstrates how optional chaining simplifies null checks:

const user = {
  name: "John",
  address: {
    street: "123 Main St",
    city: "New York",
    zip: "10001"
  }
};

// Without optional chaining
const userCity1 = user && user.address && user.address.city;

// With optional chaining
const userCity2 = user?.address?.city;

console.log(userCity1); // Output: New York
console.log(userCity2); // Output: New York

In the example above, we have an object user with nested properties. Without optional chaining, we would have to perform multiple null checks using the && operator to access the city property. However, with optional chaining, we can directly access the city property using the ?. operator, simplifying the code and reducing the chances of errors.

Optional chaining can be used with any type of object, including arrays and function calls. It provides a concise and elegant way to handle null or undefined values when accessing nested properties or methods, improving code readability and reducing potential errors.

3. Default values

In JavaScript, it is common to encounter scenarios where a variable may be null or undefined. To handle such cases, it is important to provide default values. By providing default values, we can ensure that our code continues to execute smoothly, even if a variable is null or undefined.

Providing default values is especially useful when working with function parameters. Consider the following example:

function greetUser(name) {
  name = name || 'Guest';
  console.log('Hello, ' + name + '!');
}

greetUser(); // Output: Hello, Guest!
greetUser('John'); // Output: Hello, John!

In this example, if the name parameter is not passed or is null/undefined, the default value of 'Guest' is assigned to it. This ensures that the function can execute without any issues.

Another approach to setting default values is by using the nullish coalescing operator ??. This operator allows us to provide a default value only if the variable is null or undefined. Here's an example:

const username = null;
const displayName = username ?? 'Anonymous';

console.log(displayName); // Output: Anonymous

In this example, the displayName variable is assigned the value of username only if username is not null or undefined. Otherwise, it is assigned the default value of 'Anonymous'.

Providing default values can also be achieved using the ternary operator. Here's an example:

const age = null;
const displayAge = age !== null && age !== undefined ? age : 0;

console.log(displayAge); // Output: 0

In this example, the displayAge variable is assigned the value of age if it is not null or undefined. Otherwise, it is assigned the default value of 0.

By providing default values, we can ensure that our code continues to execute without any unexpected errors, even when dealing with null or undefined values. This can greatly improve the reliability and stability of our JavaScript applications.

Conclusion

In this article, we explored the best practices for performing not null checks in JavaScript. We discussed various techniques and approaches to ensure that our code handles null or undefined values effectively.

To recap, some of the best practices include:

Using strict equality (===) or the typeof operator to check for null or undefined.
Utilizing the nullish coalescing operator (??) for concise null checks.
Creating custom null check functions for reusable and modular code.

We also explored three specific best practices in detail. The first was the early return technique, which allows us to handle null or undefined values by exiting the function early. This technique improves code readability and reduces the need for nested if statements.

The second best practice we discussed was optional chaining. This powerful feature simplifies null checks by allowing us to safely access nested properties or methods of an object without worrying about null or undefined values. It improves code readability and reduces the likelihood of runtime errors.

Lastly, we explored the concept of providing default values when a variable is null or undefined. This approach ensures that our code can handle unexpected null values by assigning a fallback value. It improves code reliability and provides a more consistent user experience.

In conclusion, thorough null checks are essential in JavaScript to prevent errors and improve code reliability. By following these best practices, we can ensure that our code handles null or undefined values effectively, leading to more robust and maintainable applications.