Optional Angular bindings

component.js

var app = angular.module('testModulePleaseIgnore', [])

app.component('legalReferences', {
  bindings: {
    foo: '&?',
    bar: '<?',
    baz: '=?',
    qux: '@?'
  },
  controller: function() {
    $ctrl.foo === undefined
    $ctrl.bar === undefined
    $ctrl.baz === undefined
    $ctrl.qux === undefined
  }
})