javascript string replace &lt; into <

You could use something like the unescapeHTML() function in prototype...

Adapted from prototype js source

function unescapeHTML(escapedHTML) {
  return escapedHTML.replace(/&lt;/g,'<').replace(/&gt;/g,'>').replace(/&amp;/g,'&');
}

Simple.

var needToConvert = 'But I want to turn "&lt;" and "&gt;" into "<" and ">".';

var convert = function(convert){
    return $("<span />", { html: convert }).text();
    //return document.createElement("span").innerText;
};

alert(convert(needToConvert));