Check if Array Doesn't contain a Value in JavaScript

# Table of Contents

1. Check if Array Doesn't contain a Value in JavaScript
2. Check if Array Doesn't contain a Value using indexOf()
3. Check if an object is not contained in an array in JavaScript

# Check if Array Doesn't contain a Value in JavaScript

Use the logical NOT (!) operator to negate the call to the includes() method to check if an array doesn't contain a value.

The negated call to the Array.includes() method will return true if the value is not in the array and false otherwise.

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const arr = ['a', 'b', 'c'];

const notIncludesD = !arr.includes('d');
console.log(notIncludesD); // 👉️ true

const notIncludesC = !arr.includes('c');
console.log(notIncludesC); // 👉️ false

if (notIncludesC) {
  console.log('✅ the value c is NOT contained in the array');
} else {
  // 👇️ this runs
  console.log('⛔️ the value c is contained in the array');
}

// ---------------------------------------

// ✅ Check if an object is not contained in an array
const arr2 = [{id: 1}, {id: 2}, {id: 3}];

const notContained = arr2.every(obj => {
  return obj.id !== 4;
});

console.log(notContained); // 👉️ true

We used the logical NOT (!) operator to negate the calls to the Array.includes() method.

This approach allows us to check if a specific value is not contained in the array.

Our first example checks if the value d is not contained in the array and returns true.

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const arr = ['a', 'b', 'c'];

const notIncludesD = !arr.includes('d');
console.log(notIncludesD); // 👉️ true

const notIncludesC = !arr.includes('c');
console.log(notIncludesC); // 👉️ false

The string c is contained in the array, so the expression returns false.

Here are some more examples of using the logical NOT (!) operator.

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console.log(!true); // 👉️ false
console.log(!false); // 👉️ true

console.log(!'hello'); // 👉️ false
console.log(!''); // 👉️ true
console.log(!null); // 👉️ true

You can imagine that the logical NOT (!) operator first converts the value to a boolean and then flips the value.

The falsy values in JavaScript are: null, undefined, empty string, NaN, 0 and false.

If you have to perform the test often, define a reusable function.

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function notIncludes(array, value) {
  return !array.includes(value);
}

const arr = ['a', 'b', 'c'];

console.log(notIncludes(arr, 'c')); // 👉️ false
console.log(notIncludes(arr, 'd')); // 👉️ true
console.log(notIncludes(arr, 'z')); // 👉️ true

The function returns true if the value is not contained in the array and false otherwise.

You can also use the indexOf() method to check if a value is not contained in an array.

# Check if Array Doesn't contain a Value using indexOf()

This is a two-step process:

1. Use the indexOf() method to get the index of the value in the array.
2. If the method returns -1, the array doesn't contain the value.

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const arr = ['a', 'b', 'c'];

if (arr.indexOf('d') === -1) {
  // 👇️ this runs
  console.log('The value d is NOT contained in the array');
} else {
  console.log('The value d is contained in the array');
}

console.log(arr.indexOf('c')); // 👉️ 2
console.log(arr.indexOf('z')); // 👉️ -1

The Array.indexOf() method returns the index of the first occurrence of the supplied value in the array.

If the value is not contained in the array, the method returns -1.

Our if statement checks if the Array.indexOf() method returned -1.

If you have to perform the test often, define a reusable function.

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function notIncludes(array, value) {
  return array.indexOf(value) === -1;
}

const arr = ['a', 'b', 'c'];

console.log(notIncludes(arr, 'c')); // 👉️ false
console.log(notIncludes(arr, 'd')); // 👉️ true
console.log(notIncludes(arr, 'z')); // 👉️ true

The function takes an array and a value as parameters and returns true if the value is not contained in the array.

If you need to check if an object is not contained in an array, use the Array.every() method.

# Check if an object is not contained in an array in JavaScript

To check if an object is not contained in an array:

1. Use the Array.every() method to iterate over the array.
2. Check if each object doesn't have a property equal to the specific value.
3. The every() method will return true if the object is not in the array.

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const arr2 = [{id: 1}, {id: 2}, {id: 3}];

const notContained = arr2.every(obj => {
  return obj.id !== 4;
});

console.log(notContained); // 👉️ true

if (notContained) {
  console.log('The object is NOT contained in the array');
} else {
  console.log('The object is contained in the array');
}

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

On each iteration, we check if the current object doesn't have a specific value and return the result.

If the callback function we passed to the Array.every() method returns a falsy value, then Array.every() short-circuits also returning false.

If the Array.every() method returns true, then the object isn't contained in the array.

If the method returns false, the object is contained in the array.