js TemplateEngine

var TemplateEngine = function(html, options) {
    var re = /<%([^%>]+)?%>/g, 
        reExp = /(^( )?(if|for|else|switch|case|break|{|}))(.*)?/g, 
        code = 'var r=[];\n', 
        cursor = 0,
        add = function(line, js) {
            js? (code += line.match(reExp) ? line + '\n' : 'r.push(' + line + ');\n') :
                (code += line != '' ? 'r.push("' + line.replace(/"/g, '\\"') + '");\n' : '');
            return add;
        };
        
    while(match = re.exec(html)) {
        add(html.slice(cursor, match.index))(match[1], true);
        cursor = match.index + match[0].length;
    }
    
    add(html.substr(cursor, html.length - cursor));
    code += 'return r.join("");';
    return new Function(code.replace(/[\r\t\n]/g, '')).apply(options);
}

http://krasimirtsonev.com/blog/article/Javascript-template-engine-in-just-20-line