[case-insensitive preg replace all] Replace all substr occurencies no matter the case ("str", <mark>str</mark> #javascript

caseInsensitivePregReplaceAll.js

function matchCase(text, pattern, tag = '') {
    var result = '';

    for(var i = 0; i < text.length; i++) {
        var c = text.charAt(i);
        var p = pattern.charCodeAt(i);

        if(p >= 65 && p < 65 + 26) {
            result += c.toUpperCase();
        } else {
            result += c.toLowerCase();
        }
    }
  
    let finalResult = result;
  if (tag) {
    finalResult = `<${tag}>${result}</${tag}>`;
  }

    return finalResult;
}

const searchQuery = 'velit';
const r = new RegExp( "(" + searchQuery + ")" , 'gi' );
const yo = "asd velitasd Velit asd".replace(r, function(match) {
    return matchCase(searchQuery, match, 'mark');
});

console.log(yo)