Need to disable g_modal submit button for the default value

[Ahsan Zafar]

Hello! I'm working on a g_modal for a workspace where I have two fields, a choicelist and textarea, in the choicelist, --None-- is the by default value, I need my SUBMIT or OK disabled when None is selected otherwise it should be enabled to submit. Here is the workspace client script, propose a solution for this requirement.
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function onClick(g_form) {

    var fields = [];

    var ga = new GlideAjax('sn_customerservice.GetDynamicChoiceList');

    ga.addParam('sysparm_name', 'getFieldChoices');

    ga.getXML(callback);

    function callback(res) {

        var result = res.responseXML.documentElement.getAttribute("answer");

        fields.push({

            type: 'choice',

            name: 'resolution_code',

            label: getMessage('Resolution Code'),

            value: getMessage(' --None-- '),

            choices: JSON.parse(result),

            mandatory: true

        });

        fields.push({

            type: 'textarea',

            name: 'close_notes',

            label: getMessage('Resolution Notes'),

            mandatory: true

        });

        g_modal.showFields({

            title: "Closure Information",

            fields: fields,

            size: 'lg',

            height: 280

        }).then(function(fieldValues) {

            g_form.setValue('resolution_code', fieldValues.updatedFields[0].value);

            g_form.setValue('close_notes', fieldValues.updatedFields[1].value);

            g_form.setValue('state',6);

            g_form.save();

        });

    }

}

 
//Thankyou..