Display form in dialog in ServiceNow and pre-populate some fields

Display form in dialog.js

function showMyForm(){
	var recordID = g_form.getUniqueValue() || "-1";
	var recordTableName = g_form.getTableName();
	var dialog = new GlideDialogForm('Update Record', recordTableName);
	
	//Set to "-1" to show new record form instead
	dialog.setSysID(recordID);
	//If false, will show related lists as well.
	dialog.addParm('sysparm_form_only', 'true');
	//todo: Form view?
	dialog.addParm('sysparm_view', 'SOME_VIEW_HERE');
	
	//From SNGuru - Thanks!
	dialog.setLoadCallback(function(iframeDoc) {
		// To get the iframe: document.defaultView in non-IE, document.parentWindow in IE
		var dialogFrame = 'defaultView' in iframeDoc ? iframeDoc.defaultView : iframeDoc.parentWindow;
		
		dialogFrame.g_form.setValue('SOME_FIELD_HERE', 'NEW_VALUE_HERE');
		dialogFrame = null;
	});
	
	//dialog.hideCloseButton(); //optional
	dialog.render();
}

showMyForm();