vCO and the parseInt JavaScript “Bug”

Today I was by a customer to develop a Custom workflow to evacuate one of his DCs with vCO. The evacuation should be done by only invoking an String into the Workflow. The Hosts were stretched over both DCs and also the Datastores. The ESX Hosts in his environment were named with vmwareXX were the XX represent a number. For the DC1 the Hosts had an even number. The Hosts in the DC2 the numbers are even.

There were hosts with names from

vmware01 till vmware24

So we developed some task to get the Datastores and the Hosts to divide them to their correct DCs. Therefore we created two Arrays were the hosts were placed for future actions. The names of the hosts were split and the Number was taken into a variable as integer. We made this with the command:

substring = parseInt(Hostname[i].substring(6,8))

After we had the number, we created an loop with if-else and placed the Hosts into the correct array.

var Odd_array = new Array ()

var Even_array = new Array()

var Nametemp

var Substring

for (i = 0; i < Hostname.length; i++) {

substring = parseInt(Hostname[i].substring(6,8))

System.log("Substring = " + substring + " Hostname = " + Hostname[i])

if (substring % 2)


//it is odd


System.log( Hostname[i] + " is in Odd Array")




//it is even


System.log( Hostname[i] + " is in even Array")



The above script generates this output.

Take a deeper look on the part with the hostnames vmware07 to vmware09. As you can see we get wrong results. The Host with the Name vmware07 was in the correct Array. The Hosts with the name vmware09 was in the even array were it was wrong.

It took some time to figure out that this is a JavaScript parseInt “Bug”. A good explanation about this behavior can be found here:

So for us the solution was to use

substring = parseInt(Hostname[i].substring(6,8), 10)

as command and everything worked like expected.

Maybe everyone expect me did not this before but this information could be useful for others so that is the reason why I created this post.

Have fun and orchestrate the World 😉