1//To do this simply create a element in the DOM tree and 
2//set the innerText of the element to your string. 
3//Then retrieve the innerHTML of the element. 
4//The browser will return an HTML encoded string.
5
6function HtmlEncode(s)
7{
8  var el = document.createElement("div");
9  el.innerText = el.textContent = s;
10  s = el.innerHTML;
11  return s;
12}
13
14console.log(HtmlEncode('&;\'><"'));
15
16//expected output: &amp;;'&gt;&lt;"

1const decodeHTML = s => {
2    var str, temp= document.createElement('p');
3    temp.innerHTML= s;
4    str= temp.textContent || temp.innerText;
5    temp=null;
6    return str;
7}
8
9console.log(decodeHTML('<'));