implement notes

assets/js/maintain_attrs.js

@@ -2,7 +2,21 @@
 // update. https://github.com/phoenixframework/phoenix_live_view/issues/1011
 
 export default {
-  attrs () { return this.el.getAttribute('data-attrs').split(', ') },
-  beforeUpdate () { this.prevAttrs = this.attrs().map(name => [name, this.el.getAttribute(name)]) },
-  updated () { this.prevAttrs.forEach(([name, val]) => this.el.setAttribute(name, val)) }
+  attrs () {
+    if (this.el && this.el.getAttribute('data-attrs')) {
+      return this.el.getAttribute('data-attrs').split(', ')
+    } else {
+      return []
+    }
+  },
+  beforeUpdate () {
+    if (this.el) {
+      this.prevAttrs = this.attrs().map(name => [name, this.el.getAttribute(name)])
+    }
+  },
+  updated () {
+    if (this.el) {
+      this.prevAttrs.forEach(([name, val]) => this.el.setAttribute(name, val))
+    }
+  }
 }