Since you're using EXT 6, I assume you're using viewcontrollers and not controllers.
Ext is going to resolve the scope as the view's controller automatically, no need to write any extra code.
First make sure you define the viewcontroller as the controller of the view:
controller: 'aliasofviewcontroller'
after that you can basically assign any of the controllers functions to the handlers of the components on the view.
Let's say you have the following function in your controller:
onClickCustomHandler:function(e){
...
}
Using the following syntax, the function is going to get called every time you're button is clicked:
Ext.create('Ext.Button', {
text: 'My button',
handler: 'onClickCustomHandler'
});
Or using xtype:
{
xtype:'button',
text:'My button',
handler: 'onClickCustomHandler'
}
For further reading: http://docs.sencha.com/extjs/6.0.2/guides/application_architecture/view_controllers.html