Ignoring Case Check if Array contains String - JavaScript

Ignoring Case Check if Array contains String - Array.findIndex #

To do a case insensitive check if an array contains a string in JavaScript:

1. Use the Array.findIndex method, passing it a function
2. The function should convert the array element and the string to lowercase and check for equality
3. If the check is successful, the element's index is returned

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// Not supported in IE 6-11
const names = ['John', 'Bob', 'Adam'];
const name = 'ADAM';

const index = names.findIndex(element => {
  return element.toLowerCase() === name.toLowerCase();
});

console.log(index); // 👉️ 2

The function we've passed to the Array.findIndex method is called with each element in the array, until the function returns a truthy value or iterates over all of the array's values.

Once the callback function returns a truthy value, the element's index is returned from findIndex.

In the code example, the function returned 2 because the 3rd element in the array matched the string.

If the function we passed to findIndex never returns a truthy value, then findIndex returns -1.

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const names = ['John', 'Bob', 'Adam'];
const name = 'Tim';

const minusOne = names.findIndex(element => {
  return element.toLowerCase() === name.toLowerCase();
});
console.log(minusOne); // 👉️ -1

Ignoring Case Check if Array contains String - Array.some #

To do a case insensitive check if an array contains a string in JavaScript:

1. Use the Array.some method, passing it a function
2. The function should convert the array element and the string to lowercase and check for equality
3. If the check succeeds, true is returned

The difference with Array.findIndex is that the Array.some method returns true or false, instead of the index of the array element or -1.

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// Supported in IE 9-11
const names = ['John', 'Bob', 'Adam'];
const name = 'JOHN';

const includesValue = names.some(element => {
  return element.toLowerCase() === name.toLowerCase();
});

console.log(includesValue); // 👉️ true

The function we passed to the Array.some method is called with each element of the array until a truthy value is returned or the array's values are exhausted.

Ignoring Case Check if Array contains String - Array.find #

1. Call the Array.find method, passing it a function
2. The function should convert the array element and the string to lowercase and check for equality
3. if the check succeeds, the array element is returned

Copied!
// Not supported in IE 6-11
const names = ['John', 'Bob', 'Adam'];
const name = 'ADAM';

const result = names.find(element => {
  return element.toLowerCase() === name.toLowerCase();
});

console.log(result); // 👉️ 'Adam'

The function we pass to the Array.find method gets called with each element in the array until it returns a truthy value or the array's values are exhausted.

If the callback function returns a truthy value, then that element is returned from the Array.find method.

If all invocations of the callback function return a falsy value, the Array.find method returns undefined.

In the code example, our case insensitive check for adam succeeded, therefore Array.find returned the array element.

Further Reading #

• Check if Array of Strings contains a Substring in JS
• Make Array.indexOf() case insensitive in JavaScript
• Ignore case of startsWith, endsWith Methods in JavaScript
• Check if Array Contains an Object in JavaScript
• Get the first N elements from an Array in JavaScript
• Get the last N elements from an Array in JavaScript