How to compare strings ignoring case

Short answer

Convert both strings to the same case and compare them:

const a = 'Hello';
const b = 'HELLO';
 
console.log(a.toLowerCase() === b.toLowerCase());

Output:

true

With localeCompare

localeCompare() returns 0 for equal strings. The option sensitivity: 'base' ignores case and accents:

console.log('Cafe'.localeCompare('café', 'en', { sensitivity: 'base' }) === 0);
console.log('apple'.localeCompare('APPLE', 'en', { sensitivity: 'base' }) === 0);

Output:

true
true

Searching ignoring case

The same idea works for searching inside a string:

const text = 'JavaScript is fun';
 
console.log(text.toLowerCase().includes('javascript'));

Output:

true

Common mistake

The == operator does not help here: it converts types, but it does not ignore case.

console.log('yes' == 'YES');

Output:

false