CODEWITHSUNDEEP
javascript
Will Fetherolf
Will Fetherolf

Reputation: 105

Why doesn't this code result in recursion?

Given this code:

function foo()
{
  if (!foo)
  {
    //blah blah blah some code here
    foo = true;
  }
}

What exactly does this do? Why is it not creating a recursive call?

Upvotes: 0

Views: 107

Answers (2)

Denys Séguret
Denys Séguret

Reputation: 382150

This might create a recursion : 

function foo()
{
  if (!foo()) // <=== notice the ()
  {
    //blah blah blah some code here
    foo = true;
  }
}

But there, without the parenthesis, foo isn't executed. The tests only checks the variable foo doesn't evaluate as true, and then replaces it with the boolean true. It's a weird code but not a recursion.

Note that we're not sure, inside the function, that foo is the function, as the code could be like this :

function foo() {
  if (!foo)
  {
    //blah blah blah some code here
    foo = true;
  }
}    
var f = foo;
foo = 0;
f(); // this would result in foo being true

Upvotes: 3

Ben McCormick
Ben McCormick

Reputation: 25728

Its not calling itself, just checking to see that a variable by that name exists/ is truthy. The function could be renamed and foo could refer to something else completely by the time it is called.

So to be clear, recursion occurs when a function calls itself

function foo(){

  foo();

}

whereas what you're doing is just looking up the current value of foo without attempting to call it.

!foo  //if foo is defined as a function or other truthy object, is true

Upvotes: 0

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