@remix-run/headers/dist/lib/header-names.js

A toolkit for working with HTTP headers in JavaScript

const HeaderWordCasingExceptions = {
    ct: 'CT',
    etag: 'ETag',
    te: 'TE',
    www: 'WWW',
    x: 'X',
    xss: 'XSS',
};
export function canonicalHeaderName(name) {
    return name
        .toLowerCase()
        .split('-')
        .map((word) => HeaderWordCasingExceptions[word] || word.charAt(0).toUpperCase() + word.slice(1))
        .join('-');
}