#Add a new link
    $url = "http://sharepoint.domain.com"
    $spWeb = Get-SPWeb -Identity "$($Url)" -ErrorAction SilentlyContinue
    # Add link
    # The format is DisplayName, link, is external (true/false)
    $node = New-Object Microsoft.SharePoint.Navigation.SPNavigationNode("Test Link", "javascript:alert('test alert')", $true)
    $spWeb.Navigation.QuickLaunch.AddAsFirst($node)
    $spWeb.Dispose()

    #Update existing link
    $spWeb = Get-SPWeb -Identity "$($Url)" -ErrorAction SilentlyContinue
    # Update link
    # Select the menu if necessary
    $selLink = $spWeb.Navigation.QuickLaunch | ? {$_.Title -eq "LinkName"}

    $selLink.Url = "javascript:alert('test')"
    $selLink.Update()

    $spWeb.Dispose()