Text Modifier

/* Write a JavaScript function fixCasing(str) that accepts a text as a parameter. The function must change
the text in all regions as follows: <upcase>text</upcase> to uppercase; <lowcase>text</lowcase> to lowercase;
<mixcase>text</mixcase> to mixed casing (randomly).
Write JS program caseFixer.js that invokes your function with the sample input data below and prints
the output at the console. */

"use strict";

function fixCasing(str) {
    var upperCaseRegex = /<upcase>(\w+\W*\w+)<\/upcase>/g;
    var match = upperCaseRegex.exec(str);
    while (match != null) {
        str = str.replace(match[0], match[1].toUpperCase());
        match = upperCaseRegex.exec(str);
    }

    var lowerCaseRegex = /<lowcase>(\w+\W*\w+)<\/lowcase>/g;
    match = lowerCaseRegex.exec(str);
    while (match != null) {
        str = str.replace(match[0], match[1].toLowerCase());
        match = lowerCaseRegex.exec(str);
    }

    function toMixCase(word) {
        var charsArr = word.split('').filter(Boolean);
        for (var i = 0; i < charsArr.length; i += 1) {
            var letter = charsArr[i];
            if (Math.round(Math.random())) {
                charsArr[i] = letter.toUpperCase();
            } else {
                charsArr[i] = letter.toLowerCase();
            }
        }

        return charsArr.join('');
    }

    var mixCaseRegex = /<mixcase>(\w+\W*\w+)<\/mixcase>/g;
    match = mixCaseRegex.exec(str);
    while (match != null) {
        str = str.replace(match[0], toMixCase(match[1]));
        match = mixCaseRegex.exec(str);
    }

    return str;
}

console.log(fixCasing(
    "We are <mixcase>living</mixcase> in a <upcase>yellow submarine</upcase>." +
    "We <mixcase>don't</mixcase> have <lowcase>anything</lowcase> else."));