How to measure code execution time in VBScript or JavaScript?

For JavaScript, use the Firebug or IE profilers, or free DynaTrace AJAX edition profiler.

For JavaScript, I would recommend you to use a profiler, like the one built-in in Firebug:

_{(source: getfirebug.com)}

Other alternatives can be the one included with Google Chrome, or IE8

If you want to do it programmatically, you could use Date objects to get a time difference:

var startTime = new Date();
// ...
// ...
var endTime = new Date();
var delta = endTime - startTime; // difference in milliseconds

Found the perfect function with proper Hours/Mins/Secs formatting here: https://social.technet.microsoft.com/wiki/contents/articles/633.vbscript-determine-script-execution-time.aspx

Usage:

dtmStartTime = Timer
Wscript.Echo "Hello, World!"
Wscript.Sleep 1000
Wscript.Echo "Script completed in " & GetElapsedTime

Function:

Function GetElapsedTime
    Const SECONDS_IN_DAY    = 86400
    Const SECONDS_IN_HOUR   = 3600
    Const SECONDS_IN_MINUTE = 60
    Const SECONDS_IN_WEEK   = 604800

    dtmEndTime = Timer

    seconds = Round(dtmEndTime - dtmStartTime, 2)
    If seconds < SECONDS_IN_MINUTE Then
        GetElapsedTime = seconds & " seconds "
        Exit Function
    End If
    If seconds < SECONDS_IN_HOUR Then 
        minutes = seconds / SECONDS_IN_MINUTE
        seconds = seconds MOD SECONDS_IN_MINUTE
        GetElapsedTime = Int(minutes) & " minutes " & seconds & " seconds "
        Exit Function
    End If
    If seconds < SECONDS_IN_DAY Then
        hours   = seconds / SECONDS_IN_HOUR
        minutes = (seconds MOD SECONDS_IN_HOUR) / SECONDS_IN_MINUTE
        seconds = (seconds MOD SECONDS_IN_HOUR) MOD SECONDS_IN_MINUTE
        GetElapsedTime = Int(hours) & " hours " & Int(minutes) & " minutes " & seconds & " seconds "
        Exit Function
    End If
    If seconds < SECONDS_IN_WEEK Then
        days    = seconds / SECONDS_IN_DAY
        hours   = (seconds MOD SECONDS_IN_DAY) / SECONDS_IN_HOUR
        minutes = ((seconds MOD SECONDS_IN_DAY) MOD SECONDS_IN_HOUR) / SECONDS_IN_MINUTE
        seconds = ((seconds MOD SECONDS_IN_DAY) MOD SECONDS_IN_HOUR) MOD SECONDS_IN_MINUTE
        GetElapsedTime = Int(days) & " days " & Int(hours) & " hours " & Int(minutes) & " minutes " & seconds & " seconds "
        Exit Function
    End If
End Function

For VBScript you can use Timer:

StartTime = Timer()
EndTime = Timer()
Response.Write("Seconds to 2 decimal places: " & FormatNumber(EndTime - StartTime, 2))

Or ASP Profiler (that is for an ASP environment.)

For JavaScript you can use Date:

var start = new Date().getTime()
alert("Milliseconds: " + (new Date().getTime() - start))

Firebug also has a profiler for JavaScript.