The datefield in Ext JS has a date picker dropdown containing a handy "Today" button, which allows you to quickly select today's date. But what if you're not interested in today's date? This post shows how you can change the text and the handler of the "Today" button in order to select a different date e.g. yesterday.
My jsfiddle for changing the "Today" button is embedded below. After the date field has been rendered, it gets a reference to the Today button via the date field's picker object and then changes its handler to select yesterday's date instead.