gistfile1.js

var Template = function(markup){ this.markup = markup; var reg_exp = /(\$[a-zA-Z0-9]+)/i } 
Template.prototype.compile = function(vars){
  this.markup = this.markup.replace(this.reg_exp, function(match){
    var key = match.substr(1, match.length-1)
    return vars[key]
  })
  return this.markup
}

/* Usage */
var t = new Template("<div class='$klass'>$content</div>")
alert(t.compile({
  klass: 'hidden',
  content: 'foo!'
}))
$('body').append(t.markup)