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Bhojendra Rauniyar

Software Engineer

Feb 19, 2019

How the recursion is working in the following code?

Can anyone please explain this code?

(function f(){
  function f(){ return 1; }
  return f();
  function f(){ return 2; }
})();

I really didn't understand the recursion. I thought it will return 1 because it already returned f(), but it returned 2.

#javascript

Responses(2)

apoorv barwa

Technology enthusiast And Web Developer

Feb 19, 2019

As said before that this is not a recurrsive problem but just how hoisting works with JS.

The code posted you would be executed in the following manner.

(function f(){
      function f(){
         return 1;
     }

     function f(){
         return 2;
     }

     return f();
})();

So when the execution reaches the return statement the definition of the function is the second one and hence your return statement is 2 and 1 will never be returned.

that's not a recursion ... that's just overriding names within a scope ...

if the interpreter would just use some type of atomic bursts without any optimizations it probably would return 1.

(function f(){
  function f(){ return 1; }
  return f();
  function f(){ return 2; }
   function f(){ return 'the function name f within this scope is overwritten again'; }
})();

Bhojendra Rauniyar an atomic burst interpreter just executes in the order of the token stream.

JS uses an AST and hoisting so it does transformations/optimizations on the AST before executing it.

this is a short summary the detailed procedures I would have to look up.

but as an example for atomic bursts -> php before version 7 did atomic bursts. I am not quite sure if that's the right word though :) they used it in the presentation of the inner architecture changes of PHP 7 maybe that's just an internal term of them.

an official term would be 'Bytecode-interpreter' although this mainly describes how it's represented and less the execution behaviour.

do I makes sense?

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How the recursion is working in the following code?

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