a simple javascript templating

tmpl.js

(function (exports) {
    var settings = {
        open: '<%',
        close: '%>',
        evaluate: '',
        interpolate: '='
    };

    var matcher = new RegExp([
        settings.open,
        '([^\\w\\s\}\)]*)\\s*(.*?)\\s*',
        settings.close
    ].join(''), 'g');

    exports.tmpl = function (str, data) {
        var source = '_p+="';
        source += str.replace(matcher, function (match, mark, code) {
            if (mark === settings.interpolate) {
                return '"+(' + code + ')+"';
            }
            if (mark === settings.evaluate) {
                return '";\n' + code + '\n_p+="';
            }
        });
        source += '";';
        source = 'var _p="";\nwith(_||{}){\n' + source + '\n}\nreturn _p;';
        var render = new Function('_', source)
        return data ? render(data) : render;
    };
})(this);

// for test
var a = this.tmpl('<span><%=a%></span>', {
    a: 1
});
console.log(a); // "<span>1</span>"

var b = this.tmpl(['<%if (typeof href !== "undefined") {%>',
    '<a href=\\"<%=href%>\\"><%=text%></a>',
    '<%} else {%>',
    '<span><%=text%></span>',
    '<%}%>'].join(''));

console.log(b({
    href: '/a.html',
    text: 'aaa'
})); // "<a href=\"/a.html\">aaa</a>"

console.log(b({
    text: 'bbb'
})); // "<span>bbb</span>"