Custom Variable Scopes

Custom variable scopes to use in your PowerShell Universal apps.

Custom Variable Scopes

Universal Apps expose three custom variable scopes using custom providers. These providers allow you to store your variables in scopes that make sense for a web application. The cache scope is used to store variables that can be used within any endpoint inside an app. The session scope is used to store variables that can be used for a single user's session of the app.

Cache Scope

Cache scope is used to store a variable that will be available in any endpoint. Cache scope is useful for storing data that may be shown in more than one control or may be time consuming to look up. This could be helpful for querying machine performance counters (e.g. Active Directory, Azure).

Just like any other scope, cache variables are defined with a prefix and a colon separator.

$Cache:Computers = Get-ADComputer

Once assigned, the $Cache:Computer variable is available within any endpoint.

New-UDMonitor -Title Computers -Endpoint {
    $Cache:Computers.Length | Out-UDMonitorData
}

Page Scope

Page scope stores variables in per browser tab or window. If a new tab is opened or the current one is closed, the state will be removed.

New-UDForm -Content {
    New-UDTextbox -Id 'Name'
} -OnSubmit {
    $Page:Name = $EventData.Name
    Sync-UDElement -Id 'Name'
}

New-UDDynamic -Content {
    New-UDTypography $Page:Name
}

Session Scope

Session scope is used to store a variable per session. A session is established when a user's browser first visit a dashboard. A cookie is stored in the user's browser that dictates that it is part of the session. Sessions have an idle timeout of 25 minutes.

Just like any other scope, cache variables are defined with a prefix and a colon separator.

New-UDCheckbox -Label "Show chart" -OnChange {
   $Session:ShowChart = $EventData
}

Once assigned, the $Session:ShowChart variable is available in app event handlers. Session variables are not available in REST API endpoints or scheduled endpoints.

New-UDColumn -Endpoint {
    if ($Session:ShowChart) {
         New-UDChart ...
    }
}

Once a session is terminated, the session variables are cleared.