Dynamically Add Missing Tags To A Broken Html String

I have a string of broken HTML. I need to search the string and add any missing opening or closing tags in JavaScript. No Regex, no jQuery. For example, I want to make a string lik

Solution 1:

Parse the string, and serialize it again. There are various ways to do this.

var str = "This <small>is <i>ONE</small> Messed up string</i>.";
str = newDOMParser().parseFromString(str, "text/html").body.innerHTML;
console.log(str);//"This <small>is <i>ONE</i></small><i> Messed up string</i>."

var str = "This <small>is <i>ONE</small> Messed up string</i>.";
var el = document.implementation.createHTMLDocument().createElement('div');
el.innerHTML = str;
str = el.innerHTML;
console.log(str);//"This <small>is <i>ONE</i></small><i> Messed up string</i>."