String reformatter

Written at 5am because I thought it was an interesting problem.

// Input:
// _string_ -> string
// *string* -> string
// [link|text] -> text, text is optional
// Handles missing links and link text
// Handles unterminated format strings

function getParts(str, endChar) {
    const uIndex = str.indexOf(endChar);
    let toProcess = "";
    if (uIndex >= 0) {
        toProcess = str.substring(0, uIndex);
        theRest = str.substring(uIndex + 1);
    } else {
        toProcess = str;
        theRest = "";
    }

    return { toProcess, theRest };
}

function formatStr(input) {
    let result = "";
    let remaining = input;
    const fmtChars = /[_*[]/;
    while (remaining) {
        let firstFmt = remaining.search(fmtChars);
        if (firstFmt < 0) {
            result += remaining;
            remaining = ""; // Done
        } else {
            result += remaining.substr(0, firstFmt);
            switch (remaining.charAt(firstFmt)) {
                case '_':
                    {
                        const { toProcess, theRest } = getParts(remaining.substr(firstFmt + 1), "_");
                        remaining = theRest;
                        result += "<em>" +
                            formatStr(toProcess) +
                            "</em>";
                    }
                    break;
                case '*':
                    {
                        const { toProcess, theRest } = getParts(remaining.substr(firstFmt + 1), "*");
                        remaining = theRest;
                        result += "<strong>" +
                            formatStr(toProcess) +
                            "</strong>";
                    }
                    break;
                case '[':
                    {
                        const { toProcess, theRest } = getParts(remaining.substr(firstFmt + 1), "*");
                        remaining = theRest;
                        const parts = toProcess.split("|", 2);
                        const link = parts.length > 0 && parts[0] ? parts[0] : "http://youforgot.com";
                        const linkText = parts.length > 1 ? parts[1] : link;
                        result += "<a href="\""" +="" link="" "\"="">" +
                            linkText +
                            "</a>";
                    }
                    break;
            }
        }
    }
    return result;
}

function test() {
    let input1 = "test _italics_ and *bold*";
    console.log(input1 + " -> " + formatStr(input1));
    let input2 = "test [link|a link] and more";
    console.log(input2 + " -> " + formatStr(input2));
    let input3 = "This is a bold italic link *_[http://example.com|to example.com]_* and some _*bold italic* italics_";
    console.log(input3 + " -> " + formatStr(input3));
    let input4 = "unterminated test *_[http://example.com|to example.com]";
    console.log(input4 + " -> " + formatStr(input4));
    let input5 = "empty link [] and partial [http//link.com] ";
    console.log(input5 + " -> " + formatStr(input5));
}