Edit in JSFiddle

angular
    .module('app', []);

// main.js
function MainCtrl() {
    this.name = 'Todd Motto';
}

angular
    .module('app')
    .controller('MainCtrl', MainCtrl);

// foo.js
function FooDirCtrl() {

}

function fooDirective() {
    
    function link($scope) {
        
    }
    
    return {
        restrict: 'E',
        scope: {
            name: '='
        },
        controller: 'FooDirCtrl',
        controllerAs: 'vm',
        template: [
            '<div><input ng-model="name"></div>'
        ].join(''),
        link: link
    };
}

angular
    .module('app')
    .directive('fooDirective', fooDirective)
    .controller('FooDirCtrl', FooDirCtrl);