var codeField = form.addField({
id: 'custpage_injectcode',
type: 'INLINEHTML',
label: 'Inject Code'
});


codeField.defaultValue = "<script>jQuery(function($){ require(['Path to your client script'], function(mod){ console.log('loaded'); mod.ClientScriptFunctionName('client_script_function_parameter');});});</script>";