Escaping HTML strings with jQuery

Since you're using jQuery, you can just set the element's text property:

// before:
// <div class="someClass">text</div>
var someHtmlString = "<script>alert('hi!');</script>";

// set a DIV's text:
$("div.someClass").text(someHtmlString);
// after: 
// <div class="someClass">&lt;script&gt;alert('hi!');&lt;/script&gt;</div>

// get the text in a string:
var escaped = $("<div>").text(someHtmlString).html();
// value: 
// &lt;script&gt;alert('hi!');&lt;/script&gt;

$('<div/>').text('This is fun & stuff').html(); // "This is fun &amp; stuff"

Source: http://debuggable.com/posts/encode-html-entities-with-jquery:480f4dd6-13cc-4ce9-8071-4710cbdd56cb

If you're escaping for HTML, there are only three that I can think of that would be really necessary:

html.replace(/&/g, "&amp;").replace(/</g, "&lt;").replace(/>/g, "&gt;");

Depending on your use case, you might also need to do things like " to ". If the list got big enough, I'd just use an array:

var escaped = html;
var findReplace = [[/&/g, "&amp;"], [/</g, "&lt;"], [/>/g, "&gt;"], [/"/g, "&quot;"]]
for(var item in findReplace)
    escaped = escaped.replace(findReplace[item][0], findReplace[item][1]);

encodeURIComponent() will only escape it for URLs, not for HTML.

Plain JavaScript escaping example:

function escapeHtml(text) {
    var div = document.createElement('div');
    div.innerText = text;
    return div.innerHTML;
}

escapeHtml("<script>alert('hi!');</script>")
// "&lt;script&gt;alert('hi!');&lt;/script&gt;"

ES6 one liner for the solution from mustache.js

const escapeHTML = str => (str+'').replace(/[&<>"'`=\/]/g, s => ({'&': '&amp;','<': '&lt;','>': '&gt;','"': '&quot;',"'": '&#39;','/': '&#x2F;','`': '&#x60;','=': '&#x3D;'})[s]);

A speed-optimized version:

function escapeHtml(s) {
   let out = "";
   let p2 = 0;
   for (let p = 0; p < s.length; p++) {
      let r;
      switch (s.charCodeAt(p)) {
         case 34: r = "&quot;"; break;  // "
         case 38: r = "&amp;" ; break;  // &
         case 39: r = "&#39;" ; break;  // '
         case 60: r = '&lt;'  ; break;  // <
         case 62: r = '&gt;'  ; break;  // >
         default: continue;
      }
      if (p2 < p) {
         out += s.substring(p2, p);
      }
      out += r;
      p2 = p + 1;
   }
   if (p2 == 0) {
      return s;
   }
   if (p2 < s.length) {
      out += s.substring(p2);
   }
   return out;
}

const s = "Hello <World>!";
document.write(escapeHtml(s));
console.log(escapeHtml(s));

For escape html specials (UTF-8)

function htmlEscape(str) {
  return str
      .replace(/&/g, '&')
      .replace(/"/g, '"')
      .replace(/'/g, ''')
      .replace(/</g, '&lt;')
      .replace(/>/g, '&gt;')
      .replace(/\//g, '&#x2F;')
      .replace(/=/g,  '&#x3D;')
      .replace(/`/g, '&#x60;');
}

For unescape html specials (UTF-8)

function htmlUnescape(str) {
  return str
      .replace(/&/g, '&')
      .replace(/"/g, '"')
      .replace(/'/g, "'")
      .replace(/&lt;/g, '<')
      .replace(/&gt;/g, '>')
      .replace(/&#x2F/g, '/')
      .replace(/&#x3D;/g, '=')
      .replace(/&#x60;/g, '`');
}