function addLogging(code) {
    var ast = esprima.parse(code);
    estraverse.traverse(ast, {
        enter: function(node, parent) {
            if (node.type === 'FunctionDeclaration' || node.type === 'FunctionExpression') {
                addBeforeCode(node);
            }
        }
    });
    return escodegen.generate(ast);
}

function addBeforeCode(node) {
    var name = node.id ? node.id.name : '<anonymous function>';
    var beforeCode = "console.log('Entering " + name + "()');";
    var beforeNodes = esprima.parse(beforeCode).body;
    node.body.body = beforeNodes.concat(node.body.body);
}