Questions #1

DBMS

• 
  What does the JOIN operator do, what types are there?
  
• 
  What does the HAVING operator do, examples?
  
• 
  When would you prefer a non-relational database?
  
• 
  What is SQL injection, what are the measures against it?
  
• 
  What is a functional index?
  
• 
  What is a transaction, its properties?
  
• 
  What is transaction scope?
  

Javascript

• 
  Difference == from ===?
  
• 
  What are closures, examples?
  
• 
  How is OOP implemented, features?
  
• 
  JSONP - what is the idea, how is it implemented
  
• 
  An error has occurred on the client, how to notify the server?
  
• 
  AT how difference between function foo() {...} and var foo = function() {...}
  
• 
  Comment out the expression:
  

(function($) {
$(function() {
alert(123);
});
})(jQuery);

• 
  Write a simple vector class (x, y) with one method.
  

Deploy

• 
  Describe the deployment scheme of a typical application. Main components.
  

Algorithms, structures

What is recursion? What are the pros, cons?
Recursion is the definition of a function in terms of itself. The logic of a recursive function usually consists of two branches. The long branch calls the same function with different parameters to accumulate the result. The short branch defines the exit criterion for the recursion.
Recursion simplifies the code and makes it declarative. Recursion encourages functional thinking and avoiding side effects.
Unoptimized recursion results in resource overhead. With a large number of iterations, you can exceed the limit on the number of recursive calls (recursion depth limit reached).
What is tail recursion?
This is a special kind of recursion, when a function ends up calling itself without additional statements. When this condition is met, the compiler unrolls the recursion into a loop with one stack frame, simply changing local variables from iteration to iteration.
For example, the classic definition of the recursive factorial return N * fact(N - 1) does not support tail recursion because the current value of N would have to be stored for each stack frame.
To make the recursion tail, accumulator parameters are added. Thanks to them, the function knows about its current state. Let the default parameter acc be 1. Then the tail-recursive notation would look like this: