JSFiddle - React, Tailwind, and code Playground

JavaScript

Ext.define('Contact', {
    extend:'Ext.data.Model',
    
    fields:[
        'first_name',
        'last_name',
        {
            name:'full_name',
            convert:function(value, record){
                return record.get('first_name') + ' ' + record.get('last_name');
            }
        }
    ]
});

Ext.application({
    launch:function(){

        var contact = Ext.create('Contact');

        contact.set('first_name', 'Neil');
        contact.set('last_name', 'McGuigan');

        var full_name = contact.get('first_name') + ' ' + contact.get('last_name');

        console.assert( contact.get('full_name') == full_name );
    }
});