tmpl.js

var cache = {}; 
function tmpl(str, data) {
    var fn = ! /\W/.test(str) ? cache[str] = cache[str] || tmpl(document.getElementById(str).innerHTML) :
        new Function("obj", "var p=[],print=function(){p.push.apply(p,arguments);};" +
        "with(obj){p.push('" +
        str.replace(/[\r\t\n]/g, " ")
        .split("<%").join("\t")
        .replace(/((^|%>)[^\t]*)'/g, "$1\r")
        .replace(/\t=(.*?)%>/g, "',$1,'")
        .split("\t").join("');")
        .split("%>")
        .join("p.push('")
        .split("\r").join("\\'") + "');}return p.join('');");
        return data ? fn(data) : fn; 
};

var a = tmpl("<div><% for(var i=0;i<10;i++){ %> <span><%= i%></span> <% } %></div>")
console.log(a)