To use Jump to URL (without javascript) you would specify the following:
=Globals!ReportServerUrl & "/Pages/ReportViewer.aspx?"
& "/Staffing/Test/Staffing Forecast Summary"
& "&rs:Command=Render"
& "&PI_REGION_LIST=" & JOIN(Parameters!PI_REGION_LIST.Value, ",")
& "&PI_CENTER_CODE=" & JOIN(Parameters!PI_CENTER_CODE.Value, ",")
& "&PI_PROBABILITY=" & JOIN(Parameters!PI_PROBABILITY.Value, ",")
& "&PI_X=" & Parameters!PI_X.Value
I've placed things on multiple lines and spaced it out to make this easier to read.
The first line specifies the Report Server URL that the original report was run on, so there's no need to hard code the production server URL.
The second line specifies the directory and report to run on the Report Server
The third line tells the Report Server what to do with the report: you could export to CSV with the following
& "&rs:Format=csv&rc:NoHeader=True&rc:Encoding=Ascii&rs:Command=Render"
The last lines specify the parameters to use. (As the first three parameters are multi-valued we join them all together, but separate them with a comma).
In changing to use the javascript functionality (from VBScript for the expression editor in the report designer) we change & for + to perform concanenation. And to explain the "?", "&", "/", "=", and " " these become %3f, %26, %2f, %3d and %20 respectively due to URL Encoding (which you can find out more here).
Unfortunately my Javascript isn't good enough to be certain of the change from VBScript to Javascript but my guess is it would go from something like this:
Globals!ReportServerUrl & "/Pages/ReportViewer.aspx?/Staffing/Test/Staffing Forecast Summary&rs:Command=Render&PI_REGION_LIST=" & JOIN(Parameters!PI_REGION_LIST.Value,",") & "&PI_CENTER_CODE=" & JOIN(Parameters!PI_CENTER_CODE.Value,",") & "&PI_PROBABILITY=" & JOIN(Parameters!PI_PROBABILITY.Value,",") & "&PI_X=" & Parameters!PI_X.Value
to this:
="javascript:void(window.open('" & Globals!ReportServerUrl & "%2fPages%2fReportViewer.aspx%3f%2fStaffing%2fTest%2fStaffing%20Forecast%20Summary%26rs:Command%3dRender%26PI_REGION_LIST%3d" & JOIN(Parameters!PI_REGION_LIST.Value,",") & "%26PI_CENTER_CODE%3d" & JOIN(Parameters!PI_CENTER_CODE.Value,",") & "%26PI_PROBABILITY%3d" & JOIN(Parameters!PI_PROBABILITY.Value,",") & "%26PI_X%3d"+Parameters!PI_X.Value & "'))"
I can't be sure of the validity of this end result in Javascript but it seems OK in the expression editor.