# Waiting for functions to complete in JavaScript

## Problem

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

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
Problem courtesy of: Sankha Narayan Guria

## Solution

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]

Fiddle

Solution courtesy of: Fabrício Matté

## Discussion

This post first appeared on Node.js Recipes, please read the originial post: here

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Waiting for functions to complete in JavaScript

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