Check if a Value is NOT in an Array using JavaScript

Check if a Value is NOT in Array #

To check if a value is not in array array, use the logical NOT (!) operator to negate a call to the includes() method, e.g. !arr.includes(myVar). The expression will return true if the value is not included in the array and false otherwise.

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

if (!arr.includes('z')) {
  console.log('✅ value is not in array');
} else {
  console.log('⛔️ value is in array');
}

We used the logical NOT (!) operator to negate a call to the Array.includes method to check if a specific value is not contained in an array.

Since we want to check if the value is not contained in the array, we have to negate (!) the result.

Here are some 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.

Falsy values are: null, undefined, empty string, NaN, 0 and false.

An alternative approach is to use the Array.indexOf method.

Check if a Value is NOT in Array using indexOf #

To check if a value is not in array array, use the indexOf() method, e.g. arr.indexOf(myVar) === -1. If the indexOf method returns -1, then the value is not contained in the array.

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// Supported in IE

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

if (arr.indexOf('z') === -1) {
  console.log('✅ value is not in array');
} else {
  console.log('⛔️ value is in array');
}

Our if statement checks if the method returned -1, if it did, we can conclude that the value is not in the array.

Further Reading #

• Check if a Value is NOT equal to 0 using JavaScript
• How to Check if a Value is a Number in JavaScript