Make includes() case insensitive in JavaScript

Make includes() case insensitive in JavaScript #

To make the String.includes() method case insensitive, convert both of the strings in the comparison to lowercase, e.g. str.toLowerCase().includes(substr.toLowerCase()). A case insensitive comparison is done by converting the two strings to the same case.

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const str = 'HELLO WORLD';
const substr = 'hELLo';

// 👇️ true
console.log(str.toLowerCase().includes(substr.toLowerCase()));

if (str.toLowerCase().includes(substr.toLowerCase())) {
  // 👉️ the substring is included in the string
}

We converted both strings to lowercase to make a case insensitive lookup using the String.includes method.

To perform a case insensitive check whether a string is contained in an array:

1. Use the Array.some() method to iterate over the array.
2. On each iteration, lowercase the current array element and the string it should be compared to.
3. The Array.some method will return true if the condition is met at least once.

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const arr = ['HELLO', 'WORLD'];
const str = 'HeLLo';

const isContained = arr.some(element => {
  return element.toLowerCase() === str.toLowerCase();
});

console.log(isContained); // 👉️ true

The function we passed to the Array.some method gets invoked with each element in the array until it returns a truthy value or iterates over all elements.

The Array.some method returns true if the callback function returns a truthy value at least once.

If all of the invocations of the function we passed to Array.some return a falsy value, the method returns false.

To perform a case insensitive check whether a string is contained in an array and get the first match:

1. Use the Array.find() method to iterate over the array.
2. On each iteration lowercase the array element and the string it should be compared to.
3. The Array.find method returns the first array element that satisfies the condition.

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const arr = ['HELLO', 'WORLD'];
const str = 'HeLLo';
const found = arr.find(element => {
  return element.toLowerCase() === str.toLowerCase();
});

console.log(found); // 👉️ HELLO

if (found !== undefined) {
  // 👉️ string is in array
}

The function we passed to the Array.find method gets invoked with each element in the array until it returns a truthy value or iterates over the entire array.

If you need to perform a case insensitive check whether a string is contained in an array and get all matches:

1. Use the Array.filter() method to iterate over the array.
2. On each iteration, lowercase the array element and the string it should be compared to.
3. The Array.filter method will return an array of all of the elements that satisfy the condition

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const arr = ['HELLO', 'HeLlO', 'WORLD'];
const str = 'HeLLo';
const matches = arr.filter(element => {
  return element.toLowerCase() === str.toLowerCase();
});

console.log(matches); // 👉️ ['HELLO', 'HeLlO']

if (matches.length > 0) {
  // 👉️ at least 1 match found in array
}

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

Further Reading #

• Check if Array of Strings contains a Substring in JS
• Replace a String case insensitive in JavaScript
• Find all Uppercase characters in a String using JavaScript
• Check if First Letter of String is Uppercase in JavaScript
• Ignore case of startsWith, endsWith Methods in JavaScript
• Make Array.indexOf() case insensitive in JavaScript
• Split a String only on the First Occurrence of a Character
• Get the first N characters of a String in JavaScript
• Get the last N characters of a String in JavaScript