use modern methods from core-js

package.json

@@ -43,6 +43,7 @@
   "dependencies": {
     "ajv": "^5.2.3",
     "babel-runtime": "^6.26.0",
+    "core-js": "^2.5.7",
     "lodash.topath": "^4.5.2",
     "prop-types": "^15.5.8",
     "setimmediate": "^1.0.5"

src/components/fields/ArrayField.js

@@ -1,5 +1,6 @@
 import React, { Component } from "react";
 import PropTypes from "prop-types";
+import includes from "core-js/library/fn/array/includes";
 
 import UnsupportedField from "./UnsupportedField";
 import {
@@ -203,7 +204,7 @@ class ArrayField extends Component {
     if (Array.isArray(itemSchema.type)) {
       // While we don't yet support composite/nullable jsonschema types, it's
       // future-proof to check for requirement against these.
-      return !itemSchema.type.includes("null");
+      return !includes(itemSchema.type, "null");
     }
     // All non-null array item types are inherently required by design
     return itemSchema.type !== "null";

src/components/widgets/SelectWidget.js

@@ -3,18 +3,16 @@ import PropTypes from "prop-types";
 
 import { asNumber } from "../../utils";
 
+const nums = new Set(["number", "integer"]);
+
 /**
  * This is a silly limitation in the DOM where option change event values are
  * always retrieved as strings.
  */
 function processValue({ type, items }, value) {
   if (value === "") {
     return undefined;
-  } else if (
-    type === "array" &&
-    items &&
-    ["number", "integer"].includes(items.type)
-  ) {
+  } else if (type === "array" && items && nums.has(items.type)) {
     return value.map(asNumber);
   } else if (type === "boolean") {
     return value === "true";

src/utils.js

@@ -1,6 +1,7 @@
 import React from "react";
 import "setimmediate";
 import validateFormData from "./validate";
+import fill from "core-js/library/fn/array/fill";
 
 const widgetMap = {
   boolean: {
@@ -155,9 +156,8 @@ function computeDefaults(schema, parentDefaults, definitions = {}) {
           if (schema.minItems > defaultsLength) {
             const defaultEntries = defaults || [];
             // populate the array with the defaults
-            const fillerEntries = new Array(
-              schema.minItems - defaultsLength
-            ).fill(
+            const fillerEntries = fill(
+              new Array(schema.minItems - defaultsLength),
               computeDefaults(schema.items, schema.items.defaults, definitions)
             );
             // then fill up the rest with either the item default or empty, up to minItems