Issue with JavaScript Recursion

Question

I'm trying to write a recursive method which may take a array/value as input and then process the input.

<html>
  <body>
    <script>
      function process(array){
        if (array instanceof Array) {
          for(i=0; i < array.length; i++){
            process(array[i]);
          }
        } else {
          document.write(array + "<br />");
        }
      }

      process([3, 4, 5, [4,1], [5,1,2],[6,1]]);
    </script>
  </body>
</html>

When I try to run this program, It seems like going to an infinite loop. Why is it?

Arun P Johny · Accepted Answer · 2010-08-15 04:34:05Z

It is because of then scope of your iteration variable "i", if you declare it as a local variable the method will work fine. ex:

for(var i=0; i < array.length; i++)

If you create a variable without the "var" keyword the scope of the variable will be global(window).

In your case when the call process([4,1]) happens the value of variable i is 3, then during the call the value of the variable "i" is rested to "0" and then incremented to "1" and "2" then the processing of value [4,1] is completed and the control is given back to the caller. But since the variable "i" is of global scope the value of "i" is modified to "2" instead of "3" so this causes the main loop to process the value [4,1] again. This leads to the infinite looping.

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