The Chrome debugger (Dev Tools) is an excellent resource but does have a learning curve. Placing console.log(yourVariableHere) in your code will display info in the console. Debugger statements should halt code execution as expected if the debugger is open (F12 on Windows). Some info on the Chrome debugger can be found in the AppStudio docs at Using the Chrome Debugger.
Though MsgBox statements display a modal dialog, code execution is not halted. Only the first dialog will display. See NSB.MsgBox for more info.
There is a way to daisy-chain your NSB.MsgBox statements together, but it requires placing them at the end of a function and then calling a response function to run when the OK button is clicked/tapped. Code execution would essentially be halted until a response is made, allowing inspection of the code in the debugger. Debugger statements might be more practical, however. The daisy chaining would look kind of look like this:
Try something like:
Dim strPoint = "5"
Dim intCnt = 3
For lngnumber = (CLng(strPoint) - (intCnt - 1)) To CLng(strPoint)
Also take a look at Conversions in the docs.