How to write a simple markdown (syntax) highlighter from scratch with javascript?

Question

I want to create a simple and fast markdown highlighter with javascript.

Input:

This is a **test bold** and __italic__ markdown. 

Output (HTML):

This is a <b>**test bold**</b> and <i>__italic__</i> markdown.

Answer 1

I'm not sure this answer is best practice and the fastest way:

let data = 'This is a **test bold** and __italic__ markdown.';
data = data.replace(/\*\*(.*?)\*\*/g, '<b>**$1**</b>');
data = data.replace(/__(.*?)__/g, '<i>__$1__</i>');