Check if an Array contains Undefined in JavaScript

# Table of Contents

1. Check if an Array contains Undefined in JavaScript
2. Check if an Array contains Undefined using Array.some()
3. Checking for undefined values that are not empty elements
4. Check if an Array contains Empty Elements in JavaScript
5. Checking only for empty elements, not undefined
6. Checking only for empty elements, not undefined using indexOf

# Check if an Array contains Undefined in JavaScript

Use the Array.includes() method to check if an array contains undefined values.

The includes method will return true if the array contains at least one undefined value and false otherwise.

Copied!
function containsUndefined(arr) {
  return arr.includes(undefined);
}

console.log(containsUndefined([1, undefined])); // 👉️ true
console.log(containsUndefined([1, 2])); // 👉️ false

The function takes an array and returns true if the array contains at least one undefined value.

The Array.includes() method takes a value and checks for its existence in the array.

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// 👇️ true
console.log([1, undefined, 3].includes(undefined));

// 👇️ false
console.log([1, 2, 3].includes(undefined));

Note that this approach would also work if there is an empty element in the array.

Copied!
function containsUndefined(arr) {
  return arr.includes(undefined);
}

console.log(containsUndefined([, 2])); // 👉️ true
console.log(containsUndefined([])); // 👉️ false

We skipped the first element in the array using a comma, however, it still counts as an undefined value.

An alternative approach is to use the Array.some() method.

# Check if an Array contains Undefined using Array.some()

This is a three-step process:

1. Use the Array.some() method to iterate over the array.
2. Compare each array element to undefined and return the result.
3. If the array contains at least one undefined value, the some() method will return true.

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function containsUndefined(arr) {
  return arr.some(element => element === undefined);
}

console.log(containsUndefined([1, undefined])); // 👉️ true
console.log(containsUndefined([1, 2])); // 👉️ false

The function we passed to the Array.some() method gets called with each element of the array.

On each iteration, we check if the current array element is equal to undefined using the strict equality (===) operator.

If the condition is met at least once, the some() method will return true.

This approach also works if the array contains empty elements.

Copied!
function containsUndefined(arr) {
  return arr.some(element => element === undefined);
}

console.log(containsUndefined([, undefined])); // 👉️ true
console.log(containsUndefined([])); // 👉️ false

# Checking for undefined values that are not empty elements

If you need to check if the array contains undefined values that are not empty elements, use the indexOf() method.

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const arr = [1, undefined, 3];

if (arr.indexOf(undefined) > -1) {
  // 👇️ this runs
  console.log('The array contains undefined values');
} else {
  console.log("The array doesn't contain undefined values");
}

The if block will only run if the array contains undefined values that are not empty elements.

The Array.includes() method returns true if the array contains empty elements or undefined values (or both).

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const arr = [1, , 3];

console.log(arr.includes(undefined)); // 👉️ true

The array doesn't contain any undefined values but has an empty element, so the includes() method returns true.

# Check if an Array contains Empty Elements in JavaScript

Use the Array.includes() method to check if an array contains empty elements.

The Array.includes() method will return true if the array contains empty elements and false otherwise.

Copied!
const arr = [1, , 3];

console.log(arr[1]); // 👉️ undefined

console.log(arr.includes(undefined)); // 👉️ true

if (arr.includes(undefined)) {
  console.log(`✅ array contains an empty element(s)
               or undefined value(s)`);
} else {
  console.log(`⛔️ array DOESN'T contain an empty
               element or undefined value`);
}

We have an empty element in the array at index 1. If we try to access the element, we get a value of undefined back.

Copied!
const arr = [1, , 3];

console.log(arr[1]); // 👉️ undefined

We used the Array.includes() method to check if the array contains undefined values.

Note that this check would also pass if the array contains an element with a value of undefined.

Copied!
const arr = [1, undefined , 3];

console.log(arr.includes(undefined)); // 👉️ true

# Checking only for empty elements, not undefined

If you need to make sure the array contains an empty element and not undefined values, use this approach instead.

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function containsEmptyElements(arr) {
  return Object.values(arr).length !== arr.length;
}

// 👇️ true
console.log(containsEmptyElements([1, 2, , 4]));

// 👇️ false
console.log(containsEmptyElements([1, 2, undefined, 4]));

We passed the array to the Object.values() method.

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// [ 1, 2, 4 ]
console.log(Object.values([1, 2, , 4]));

// [ 1, 2, undefined, 4 ]
console.log(Object.values([1, 2, undefined, 4]));

Notice that empty elements get removed in the call to Object.values() but undefined values don't.

If the length of the array the Object.values() method returns is not equal to the length of the array, then the array contains empty elements.

# Checking only for empty elements, not undefined using indexOf

You can also use the Array.indexOf() method to check if the array contains empty elements.

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function containsEmptyElements(arr) {
  return arr.indexOf(undefined) === -1 && arr.includes(undefined);
}

const arr = [1, 2, , 4];

console.log(containsEmptyElements(arr)); // 👉️ true

if (containsEmptyElements(arr)) {
  // 👇️ this runs
  console.log('✅ The array contains empty element(s)');
} else {
  console.log("⛔️ The array DOESN'T contain empty elements");
}

We used the logical AND (&&) operator to chain multiple conditions.

The if statement checks if the Array.indexOf() method returns -1 and the array contains undefined values.

This check would only succeed if the array has one or more empty elements.

The Array.indexOf() method returns -1 only when it doesn't find the supplied value.

This is why the indexOf method doesn't find an element with the value of undefined in the array.

If both of the conditions are met, the array contains one or more empty elements.

# Additional Resources

You can learn more about the related topics by checking out the following tutorials:

• Check if Array contains only Numbers in JavaScript
• Check if an Array contains Duplicates in JavaScript
• Check if Array Contains an Object in JavaScript