Explicitly throw if the rest/spread items are not iterable.

packages/babel-helpers/src/helpers.js

@@ -687,17 +687,21 @@ helpers.slicedToArrayLoose = () => template.program.ast`
 
 helpers.toArray = () => template.program.ast`
   import arrayWithHoles from "arrayWithHoles";
+  import iterableToArray from "iterableToArray";
+  import nonIterableRest from "nonIterableRest";
 
   export default function _toConsumableArray(arr) {
-    return arrayWithHoles(arr) || Array.from(arr);
+    return arrayWithHoles(arr) || iterableToArray(arr) || nonIterableRest();
   }
 `;
 
 helpers.toConsumableArray = () => template.program.ast`
   import arrayWithoutHoles from "arrayWithoutHoles";
+  import iterableToArray from "iterableToArray";
+  import nonIterableSpread from "nonIterableSpread";
 
   export default function _toConsumableArray(arr) {
-    return arrayWithoutHoles(arr) || Array.from(arr);
+    return arrayWithoutHoles(arr) || iterableToArray(arr) || nonIterableSpread();
   }
 `;
 
@@ -716,6 +720,15 @@ helpers.arrayWithHoles = () => template.program.ast`
   }
 `;
 
+helpers.iterableToArray = () => template.program.ast`
+  export default function _iterableToArray(iter) {
+    if (
+      Symbol.iterator in Object(iter) ||
+      Object.prototype.toString.call(iter) === "[object Arguments]"
+    ) return Array.from(iter);
+  }
+`;
+
 helpers.iterableToArrayLimit = () => template.program.ast`
   export default function _iterableToArrayLimit(arr, i) {
     // this is an expanded form of \`for...of\` that properly supports abrupt completions of
@@ -762,6 +775,12 @@ helpers.iterableToArrayLimitLoose = () => template.program.ast`
   }
 `;
 
+helpers.nonIterableSpread = () => template.program.ast`
+  export default function _nonIterableSpread() {
+    throw new TypeError("Invalid attempt to spread non-iterable instance");
+  }
+`;
+
 helpers.nonIterableRest = () => template.program.ast`
   export default function _nonIterableRest() {
     throw new TypeError("Invalid attempt to destructure non-iterable instance");