Hello all,

Can someone explain the attached code please..And in particular, how the program execution flows between the different scope blocks.. Thanks

<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en">
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<script type="text/javascript">

function runRecursion() {

   var addNumbers = function sumNumbers(numArray,indexVal,resultArray) {
      // recursion test
      if (indexVal == numArray.length) 
         return resultArray;

      // perform numeric addition
      resultArray[0] += Number(numArray[indexVal]);

      // perform string concatenation 
      if (resultArray[1].length > 0) { 
         resultArray[1] += " and ";
      resultArray[1] += numArray[indexVal].toString();
      // increment index

      // call function again, return results
      return sumNumbers(numArray,indexVal,resultArray);

   // create numeric array, and the result array
   var numArray = ['1','35.4','-14','44','0.5'];
   var resultArray = new Array(0,''); // necessary for the initial case

   // call function
   var result = addNumbers(numArray,0, resultArray);

   // output
   document.writeln(result[0] + "<br />");
<body onload="runRecursion();">
6 Years
Discussion Span
Last Post by Troy III

The code is finding sum of array values using recursive method

var numArray = ;
Here you can change the values and check the result. as it is called onload, everytime you have to open link in fresh page, refresh may not work

functions accepts 3 arguments, data array, current array index, and result array

function checks if current index is >= to lenght then it returns to calling part.
other wise it adds current index array value to 0th index of result array
it also build a string of array values and store in 1st index of result array.

Now index value is increment and again same function is called with incremented index value.

Edited by urtrivedi: n/a



Scopes here are maybe not obvious.

The outer function forms a "closure" giving each instance of the inner function access to numAray , resultArray and result .

In javascript, objects (including arrays) are equated and passed by reference (not by value). Consequently:

  • the formal parameters numArray and resultArray are actually references to the original arrays declared in the outer function
  • numArray and resultArray need not be formally passed.

Meanwhile, numbers and strings are equated and passed by value (not by reference).

Taking advantage of this knowledge (and by rearranging things a bit), the code can be considerably simplified:

<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en">
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<script type="text/javascript">
onload = function() {
   var numArray = [1, 35.4, -14, 44, 0.5];
   function addNumbers(total, indexVal) {
      return (indexVal >= numArray.length) ? total : addNumbers(total+numArray[indexVal], ++indexVal);
   document.writeln(addNumbers(0, 0) + '<br />' + numArray.join(' and ');


Edited by Airshow: n/a


Nice construction Airshow, that's efficient coding;
for further optimization purposes the function recursion can also be omitted I think:

var args=[1,35.4,-14,44,0.5];
document.writeln(function(args,x,v){for(x in args)v+=args[x];return v+"<br>"+args.join(' and ')}(args,0,0))

Whoops, there's mistake in my code.

document.writeln(addNumbers(0, 0) + '<br />' + numArray.join(' and ');
document.writeln(addNumbers(0, 0) + '<br />' + numArray.join(' and '));



Yeah, you forgot to close the writeln( [...] ; but that's not a big deal. Your literal conditional has found a very elegant use of a recursive call there.

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