Understanding recursion [closed]

Answer 1

I think this very simple method should help you understand recursion. The method will call itself until a certain condition is true and then return:

function writeNumbers( aNumber ){
 write(aNumber);
 if( aNumber > 0 ){
  writeNumbers( aNumber - 1 );
 }
 else{
  return;
 }
}

This function will print out all numbers from the first number you'll feed it till 0. Thus:

writeNumbers( 10 );
//This wil write: 10 9 8 7 6 5 4 3 2 1 0
//and then stop because aNumber is no longer larger then 0

What bassicly happens is that writeNumbers(10) will write 10 and then call writeNumbers(9) which will write 9 and then call writeNumber(8) etc. Until writeNumbers(1) writes 1 and then calls writeNumbers(0) which will write 0 butt will not call writeNumbers(-1);

This code is essentially the same as:

for(i=10; i>0; i--){
 write(i);
}

Then why use recursion you might ask, if a for-loop does essentially the same. Well you mostly use recursion when you would have to nest for loops but won't know how deep they are nested. For example when printing out items from nested arrays:

var nestedArray = Array('Im a string', 
                        Array('Im a string nested in an array', 'me too!'),
                        'Im a string again',
                        Array('More nesting!',
                              Array('nested even more!')
                              ),
                        'Im the last string');
function printArrayItems( stringOrArray ){
 if(typeof stringOrArray === 'Array'){
   for(i=0; i

This function could take an array which could be nested into a 100 levels, while you writing a for loop would then require you to nest it 100 times:

for(i=0; i

As you can see the recursive method is a lot better.