Make includes() case insensitive in JavaScript

Make includes() case insensitive in JavaScript #

To make the String.includes() method case insensitive in JavaScript, convert both of the strings you're comparing to lowercase.

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// not supported in IE 6-11
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
}

In the code example we've converted both - the string we call String.includes on and the substring to lowercase to make a case insensitive lookup.

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

1. call the Array.find method, passing it a function
2. the function should lowercase the array element and the string and do an equality check
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 all elements.

In the code example, the case insensitive check for the string succeeded and Array.find returned the corresponding array element.

If all of the invocations of the function we passed to Array.find return a falsy value, then the method returns undefined.

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

1. call the Array.filter method, passing it a function
2. the function should lowercase the array element and the string and do an equality check
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.

In our case two elements of the array satisfy the condition and we have both of their values in a brand new 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