maintain focus on open modals

js/mixins/modal.js

@@ -1,17 +1,32 @@
+import ally from 'ally.js'
+
 export default {
   methods: {
     closeModal: function(name) {
       this.activeModal = null
       this.$emit('modalOpen', false)
+      if (this.allyHandler) this.allyHandler.disengage()
     },
+
     openModal: function (name) {
       this.activeModal = name
       this.$emit('modalOpen', true)
+      const idSelector = `#${this.modalId}`
+
+      this.allyHandler = ally.maintain.disabled({
+        filter: idSelector
+      });
     }
   },
   data: function() {
     return {
       activeModal: null,
+      allyHandler: null
+    }
+  },
+  computed: {
+    modalId: function () {
+      return !!this.activeModal ? `modal--${ this.activeModal }` : null
     }
   }
 }