N/ui/serverWidget Module
Field.defaultValue
Property Description: The default value for this field. If you pass an empty string or any value that is not a number, such as undefined, the field defaults to a blank field in the UI. This property is supported only on scripted fields created using the N/ui/serverWidget Module.
Type: string
Supported Script Types: SuiteScript 2.0 Suitelet Script Type and SuiteScript 2.0 User Event Script Type (beforeLoad(scriptContext))
Module: N/ui/serverWidget Module
Since: 2015.2
Search NetSuite - https://system.netsuite.com/app/help/helpcenter.nl?search=Field.defaultValue

// Code Example 1

//Add additional code

//...

var form = serverWidget.createForm({

    title : 'Simple Form'

});

var field = form.addField({

    id : 'custpage_textfield',

    type : serverWidget.FieldType.TEXT,

    label : 'Text'

});

field.defaultValue = 'Insert Text Here.';

//...

//Add additional code



//SOURCE: https://system.netsuite.com/app/help/helpcenter.nl?fid=section_4335275520.html