Check if a String is contained in an Array in JavaScript

Check if a String is contained in an Array #

To check if a string is contained in an array, call the includes() method, passing it the string as a parameter. The includes method will return true if the string is contained in the array and false otherwise.

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const arr = ['one', 'two', 'three'];

if (arr.includes('two')) {
  console.log('✅ String is contained in Array');
} else {
  console.log('⛔️ String is NOT contained in Array');
}

We used the Array.includes method to check if the string two is contained in the array.

Note that the includes method performs a case-sensitive comparison.

If you need to perform a case-insensitive check whether a string is contained in an array, use the Array.some method.

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const arr = ['one', 'two', 'three'];

const two = 'TWO';

const containsString = arr.some(element => {
  return element.toLowerCase() === two.toLowerCase();
});

console.log(containsString); // 👉️ true

We used the toLowerCase() method to lowercase the array element and the string to perform a case-insensitive comparison.

If the function we passed to the some() method returns a truthy value at least once, the method short-circuits and returns true.

You can also use the indexOf method as an alternative to includes().

Check if a String is contained in an Array using indexOf #

To check if a string is contained in an array, call the indexOf method, passing it the string as a parameter. The indexOf method returns the index of the first occurrence of the string in the array, or -1 if the string is not contained in the array.

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const arr = ['one', 'two', 'three'];

if (arr.indexOf('two') !== -1) {
  console.log('✅ String is contained in Array');
} else {
  console.log('⛔️ String is NOT contained in Array');
}

We used the Array.indexOf method to check if the string two is contained in the array.

Which approach you pick is a matter of personal preference. I'd go with using the includes() method as I find it more readable and direct.

Further Reading #

• Check if a String is contained in an Array in JavaScript
• Check if String contains Substring from Array in JavaScript