Markdown

function wrap(text, tag) {return <${tag}>${text}</${tag}>;}

function isTag(text, tag) {return text.startsWith(<${tag}>);}

function parser(markdown, delimiter, tag) {return markdown.replace(new RegExp(${delimiter}(.+)${delimiter}), <${tag}>$1</${tag}>);}

function parse__(markdown) {return parser(markdown, '__', 'strong');}

function parse_(markdown) {return parser(markdown, '_', 'em');}

function parseText(markdown, list) {if (list) {return parse_(parse__(markdown));} else {return wrap(parse_(parse__(markdown)), 'p');}}

function parseHeader(markdown, list) {
let count = 0;
for (let i = 0; i < markdown.length; i++) {
if(markdown[i] === '#'){count += 1;}
else {break;}
}
if (count === 0 || count > 6) {return [null, list]; }
const headerHtml = wrap(markdown.substring(count + 1), h${count});
return list? [</ul>${headerHtml}, false]: [headerHtml, false];
}

function parseLineItem(markdown, list) {
if (markdown.startsWith('*')) {
const innerHtml = wrap(parseText(markdown.substring(2), true), 'li');
return (list) ? [innerHtml, true]:[<ul>${innerHtml}, true];
}
return [null, list];
}

function parseParagraph(markdown, list) {return (!list)? [parseText(markdown, false), false]: [</ul>${parseText(markdown, false)}, false];}

function parseLine(markdown, list) {
let [result, inListAfter] = parseHeader(markdown, list);
if (result === null) {[result, inListAfter] = parseLineItem(markdown, list);}
if (result === null) {[result, inListAfter] = parseParagraph(markdown, list);}
if(result === null) {throw new Error('Invalid markdown');}
return [result, inListAfter];
}

export function parse(markdown) {
const lines = markdown.split('\n');
let result = '';
let list = false;
for (let i = 0; i < lines.length; i++) {
let [lineResult, newList] = parseLine(lines[i], list);
result += lineResult;
list = newList;
}
return (list)? result + '': result;
}