compute is a convenience method for making computes from properties of Observes. More information about computes can be found under [can.compute].

var map = new Map({a: 'Alexis'});
var name = map.compute('a');
name.bind('change', function(ev, nevVal, oldVal) {
    console.log('a changed from ' + oldVal + 'to' + newName + '.');
});

name(); // 'Alexis'

map.attr('a', 'Adam'); // 'a changed from Alexis to Adam.'
name(); // 'Adam'

name('Alice'); // 'a changed from Adam to Alice.'
name(); // 'Alice'