Like PHP's htmlentities()/htmlspecialchars() functions, JavaScript is easy to implement it.
/**
 * HTML entities encode
 *
 * @param {string} str Input text
 * @return {string} Filtered text
 */
function htmlencode (str){
  var div = document.createElement('div');
  div.appendChild(document.createTextNode(str));
  return div.innerHTML;
}jQuery implementation:
return $("<div/>").text(str).html();
/**
 * HTML entities decode
 *
 * @param {string} str Input text
 * @return {string} Filtered text
 */
function htmldecode (str){
  var txt = document.createElement('textarea');
  txt.innerHTML = str;
  return txt.value;
}jQuery implementation:
return $("<div/>").html(str).text();
In general, most Front-End development doesn't require encode/decode functions, you can evaluate your scenario to confirm the need for use.