Small templating function

tmpl.js

// Use `<% ... %>` to execute blocks of JavaScript, `<%= ... %>` to write
// out the result of the embedded expression.
function tmpl(str, params) {
    if (!str) return '';
    
    function generateOutput(str) {
        return "  p.push('" + str.replace(/'/g, "\\'").split(/\r?\n/g).join("\\n');\n  p.push('") + "');\n";
    }

    var fn;
    if (str.indexOf('<%') == -1) {
        fn = function() { return str; };
    } else {
        var fragments = str.split(/<%\s*|\s*%>/g),
            body = 'var p = []; with(o) {\n',
            insideExpression = false;

        fragments.forEach(function(frag) {
            if (insideExpression) {
                if (frag[0] == '=') {
                    // it's an expression, so output its value
                    body += "  p.push(" + frag.replace(/^=\s*|\s*$/g, '') + ");\n";
                } else {
                    // it's a JavaScript statement
                    body += "  " + frag + '\n';
                }
            } else if (frag) {
                // literal string, just escape
                body += generateOutput(frag);
            }
            insideExpression = !insideExpression;
        });

        body += '} return p.join("");';

        try {
            fn = new Function('o', body);
        } catch(ex) {
            var err = new Error('Cannot parse template! (see `template` property)');
            err.template = body;
            throw err;
        }
    }

    return params ? fn(params) : fn;
}