Client Script why can't use g_form.getQueryParameter

[KelvinY2025]

function onLoad() {
var myparam = g_form.getQueryParameter('myparam');

....
}

why ? 
(g_env) [SCRIPT:EXEC] Error while running Client Script "Incident Demo01": TypeError: g_form.getQueryParameter is not a function

how to do ?

[KelvinY2025]

function onLoad() {

    // var myparam = g_url.getParameter('myparam');

    var myparam = g_form.getParameter('myparam');

    console.log(myparam);

}

Used under sow, it doesn't work