Call out to various http(s) endpoints to determine if you can access the web.

Test-IsOnline.ps1

function Test-IsOnline {
    param([Alias('t', 'timeout', 'timeout-secs')][int] $timeout_secs)
    $urls = 'https://google.com/generate_204', `
        'http://google.com/generate_204', `
        'https://edge-http.microsoft.com/captiveportal/generate_204', # not sure if MS supports https?
        'http://edge-http.microsoft.com/captiveportal/generate_204', `
        'https://connectivity-check.ubuntu.com', `
        'https://connectivity-check.ubuntu.com'
    $okcodes = '204', '200'    # above URLs should always return 204
    if ($timeout_secs -lt 0) { $timeout_secs = 0 }
    foreach ($url in $urls) {
        $response = $(curl --silent --write-out "%{http_code}" --max-time $timeout_secs $url)
        if ($response -in $okcodes) { return $true }
    }
    return $false
}
#set-alias isonline Test-IsOnline

Test-IsOnline