Waiting for functions to complete in JavaScript

Question

Waiting for functions to complete in JavaScript

How come the following code, generates a different output everytime (not because of the random function) but it gives undefined for some values, sometimes some others. What is the problem?

function getRandom(ubound) {
  return Math.floor((Math.random()*10) % ubound); 
}

function getInterval() {
  var interval = [getRandom(10), getRandom(10)];
  if(interval[1] >= interval[0])
    return interval;
  else
    getInterval();
}

function generateIntervals() {
  for(var i = 0; i < n; i++)
    intervals[i] = getInterval();
}

function printIntervals() {
  for(var i = 0; i < n; i++)
    console.log("Node " + (i + 1) + ": " + intervals[i]);
}

generateIntervals();
printIntervals();

I get outputs like:

Node 1: 0,9
Node 2: 0,3
Node 3: undefined
Node 4: 2,2

or

Node 1: 3,3
Node 2: 3,3
Node 3: 1,8
Node 4: undefined

javascript
node.js
recursion

Answer 1

Missing a return in your recursive function:

if(interval[1] >= interval[0])
    return interval;
else
    return getInterval();
//  ^^^^^^

Though I'd personally just swap the 2 values around instead of using recursion for that. =]

if(interval[1] >= interval[0])
    return interval;
else
    return [interval[1], interval[0]];

Or more simply/semantic using Array.reverse():

if(interval[1] < interval[0])
    interval.reverse();
return interval;

Fiddle