function allKeys(obj) {  
    if (!isObject(obj)) return [];  
    var keys = [];  
    for (var key in obj) keys.push(key);  
    return keys;  
}  
function isObject(obj)   
{  
    var type = typeof obj;  
    return type === 'function' || type === 'object' && !!obj;  
  }  
function Student(name) {  
  this.name = name;  
}  
Student.prototype.rollno = true;  
console.log(allKeys(new Student("Sara")));