Drop core-js in favour of custom fallbacks

Ref atlassian/react-beautiful-dnd#1629 (comment)

I forbid using es6+ methods I added eslint-plugin-es6. It does not
forbid isInteger but I send PR nkt/eslint-plugin-es5#37.

.eslintrc.js

@@ -17,6 +17,7 @@ module.exports = {
     'react-hooks',
     'import',
     'jest',
+    'es5',
   ],
   env: {
     es6: true,
@@ -62,7 +63,7 @@ module.exports = {
     'no-plusplus': 'off',
 
     // Always enforcing the use of curly braces for if statements
-    'curly': ['error', 'all'],
+    curly: ['error', 'all'],
 
     'no-restricted-syntax': [
       // Nicer booleans #1
@@ -102,14 +103,16 @@ module.exports = {
       // No usage of `tiny-invariant`. Must use our own invariant for error flow
       {
         selector: 'ImportDeclaration[source.value="tiny-invariant"]',
-        message: 'Please use our own invariant function (src/invariant.js) to ensure correct error flow'
+        message:
+          'Please use our own invariant function (src/invariant.js) to ensure correct error flow',
       },
 
       // Must use invariant to throw
       {
         selector: 'ThrowStatement',
-        message: 'Please use invariant (src/invariant.js) for throwing. This is to ensure correct error flows'
-      }
+        message:
+          'Please use invariant (src/invariant.js) for throwing. This is to ensure correct error flows',
+      },
     ],
 
     // Allowing Math.pow rather than forcing `**`
@@ -206,4 +209,14 @@ module.exports = {
     // don't need to initialize state in a constructor
     'react/state-in-constructor': 'off',
   },
+  overrides: [
+    // Forbid using not es5 methods
+    {
+      files: 'src/**/*.js',
+      rules: {
+        'es5/no-es6-methods': 'error',
+        'es5/no-es6-static-methods': 'error',
+      },
+    },
+  ],
 };

.size-snapshot.json

@@ -1,25 +1,25 @@
 {
   "dist/react-beautiful-dnd.js": {
-    "bundled": 379875,
-    "minified": 139571,
-    "gzipped": 41966
+    "bundled": 365555,
+    "minified": 134065,
+    "gzipped": 39834
   },
   "dist/react-beautiful-dnd.min.js": {
-    "bundled": 321489,
-    "minified": 115006,
-    "gzipped": 34084
+    "bundled": 307334,
+    "minified": 109550,
+    "gzipped": 31958
   },
   "dist/react-beautiful-dnd.esm.js": {
-    "bundled": 241086,
-    "minified": 125714,
-    "gzipped": 32875,
+    "bundled": 241599,
+    "minified": 125790,
+    "gzipped": 32910,
     "treeshaked": {
       "rollup": {
-        "code": 21306,
-        "import_statements": 788
+        "code": 21158,
+        "import_statements": 503
       },
       "webpack": {
-        "code": 24963
+        "code": 24653
       }
     }
   }

package.json

@@ -56,7 +56,7 @@
     "prepublishOnly": "yarn build"
   },
   "dependencies": {
-    "@babel/runtime-corejs2": "^7.6.3",
+    "@babel/runtime": "^7.6.3",
     "css-box-model": "^1.2.0",
     "memoize-one": "^5.1.1",
     "raf-schd": "^4.0.2",
@@ -96,6 +96,7 @@
     "eslint-config-prettier": "^6.4.0",
     "eslint-plugin-cypress": "^2.7.0",
     "eslint-plugin-emotion": "^10.0.14",
+    "eslint-plugin-es5": "^1.4.1",
     "eslint-plugin-flowtype": "^4.3.0",
     "eslint-plugin-import": "^2.18.2",
     "eslint-plugin-jest": "^22.20.0",

rollup.config.js

@@ -20,7 +20,7 @@ const excludeAllExternals = id => !id.startsWith('.') && !id.startsWith('/');
 const getBabelOptions = ({ useESModules }) => ({
   exclude: 'node_modules/**',
   runtimeHelpers: true,
-  plugins: [['@babel/transform-runtime', { corejs: 2, useESModules }]],
+  plugins: [['@babel/transform-runtime', { useESModules }]],
 });
 
 const snapshotArgs =

src/native-with-fallback.js

@@ -1,14 +1,30 @@
 // @flow
+/* eslint-disable es5/no-es6-methods */
+
 type Map<T> = {
   [key: string]: T,
 };
 
-// @babel/runtime-corejs2 will replace Object.values
+// Number.isInteger is not forbidden yet
+// https://github.com/nkt/eslint-plugin-es5/pull/37
+export function isInteger(value: mixed): boolean {
+  if (Number.isInteger) {
+    return Number.isInteger(value);
+  }
+  return (
+    typeof value === 'number' && isFinite(value) && Math.floor(value) === value
+  );
+}
+
 // Using this helper to ensure there are correct flow types
 // https://github.com/facebook/flow/issues/2221
 export function values<T>(map: Map<T>): T[] {
-  // $FlowFixMe - Object.values currently does not have good flow support
-  return Object.values(map);
+  if (Object.values) {
+    // $FlowFixMe - Object.values currently does not have good flow support
+    return Object.values(map);
+  }
+
+  return Object.keys(map).map(key => map[key]);
 }
 
 // Could also extend to pass index and list

src/view/assign-visually-hidden-style.js

@@ -0,0 +1,16 @@
+// @flow
+// https://allyjs.io/tutorials/hiding-elements.html
+// Element is visually hidden but is readable by screen readers
+const assignVisuallyHidden = (style: Object) => {
+  style.position = 'absolute';
+  style.width = '1px';
+  style.height = '1px';
+  style.margin = '-1px';
+  style.border = '0';
+  style.padding = '0';
+  style.overflow = 'hidden';
+  style.clip = 'rect(0 0 0 0)';
+  style['clip-path'] = 'inset(100%)';
+};
+
+export default assignVisuallyHidden;

src/view/draggable/use-validation.js

@@ -1,6 +1,7 @@
 // @flow
 import { useRef } from 'react';
 import { invariant } from '../../invariant';
+import { isInteger } from '../../native-with-fallback.js';
 import type { DraggableId, ContextId } from '../../types';
 import type { Props } from './draggable-types';
 import checkIsValidInnerRef from '../check-is-valid-inner-ref';
@@ -21,7 +22,6 @@ export function useValidation(
 
     // wrapping entire block for better minification
     const id: ?DraggableId = props.draggableId;
-    // Number.isInteger will be provided by @babel/runtime-corejs2
     invariant(id, 'Draggable requires a draggableId');
     invariant(
       typeof id === 'string',
@@ -30,7 +30,7 @@ export function useValidation(
     );
 
     invariant(
-      Number.isInteger(props.index),
+      isInteger(props.index),
       `${prefix(id)} requires an integer index prop`,
     );
 

src/view/use-announcer/use-announcer.js

@@ -4,7 +4,7 @@ import { useMemo, useCallback } from 'use-memo-one';
 import type { Announce, ContextId } from '../../types';
 import { warning } from '../../dev-warning';
 import getBodyElement from '../get-body-element';
-import visuallyHidden from '../visually-hidden-style';
+import assignVisuallyHidden from '../assign-visually-hidden-style';
 
 export const getId = (contextId: ContextId): string =>
   `rbd-announcement-${contextId}`;
@@ -31,7 +31,7 @@ export default function useAnnouncer(contextId: ContextId): Announce {
       el.setAttribute('aria-atomic', 'true');
 
       // hide the element visually
-      Object.assign(el.style, visuallyHidden);
+      assignVisuallyHidden(el.style);
 
       // Add to body
       getBodyElement().appendChild(el);

src/view/use-lift-instruction/use-lift-instruction.js

@@ -25,7 +25,7 @@ export default function useLiftInstruction(
 
       // Using `display: none` prevent screen readers from reading this element in the document flow
       // This element is used as a `aria-labelledby` reference for *other elements* and will be read out for those
-      Object.assign(el.style, { display: 'none' });
+      el.style.display = 'none';
 
       // Add to body
       getBodyElement().appendChild(el);

yarn.lock

@@ -992,14 +992,6 @@
     "@babel/helper-plugin-utils" "^7.0.0"
     "@babel/plugin-transform-typescript" "^7.6.0"
 
-"@babel/runtime-corejs2@^7.6.3":
-  version "7.6.3"
-  resolved "https://registry.yarnpkg.com/@babel/runtime-corejs2/-/runtime-corejs2-7.6.3.tgz#de3f446b3fb688b98cbd220474d1a7cad909bcb8"
-  integrity sha512-nuA2o+rgX2+PrNTZ063ehncVcg7sn+tU71BB81SaWRVUbGwCOlb0+yQA1e0QqmzOfRSYOxfvf8cosYqFbJEiwQ==
-  dependencies:
-    core-js "^2.6.5"
-    regenerator-runtime "^0.13.2"
-
 "@babel/runtime@7.3.4":
   version "7.3.4"
   resolved "https://registry.yarnpkg.com/@babel/runtime/-/runtime-7.3.4.tgz#73d12ba819e365fcf7fd152aed56d6df97d21c83"
@@ -1021,6 +1013,13 @@
   dependencies:
     regenerator-runtime "^0.13.2"
 
+"@babel/runtime@^7.6.3":
+  version "7.8.3"
+  resolved "https://registry.yarnpkg.com/@babel/runtime/-/runtime-7.8.3.tgz#0811944f73a6c926bb2ad35e918dcc1bfab279f1"
+  integrity sha512-fVHx1rzEmwB130VTkLnxR+HmxcTjGzH12LYQcFFoBwakMd3aOMD4OsRN7tGG/UOYE2ektgFrS8uACAoRk1CY0w==
+  dependencies:
+    regenerator-runtime "^0.13.2"
+
 "@babel/template@^7.1.0", "@babel/template@^7.4.0", "@babel/template@^7.4.4", "@babel/template@^7.6.0":
   version "7.6.0"
   resolved "https://registry.yarnpkg.com/@babel/template/-/template-7.6.0.tgz#7f0159c7f5012230dad64cca42ec9bdb5c9536e6"
@@ -4048,7 +4047,7 @@ core-js@^1.0.0:
   resolved "https://registry.yarnpkg.com/core-js/-/core-js-1.2.7.tgz#652294c14651db28fa93bd2d5ff2983a4f08c636"
   integrity sha1-ZSKUwUZR2yj6k70tX/KYOk8IxjY=
 
-core-js@^2.4.0, core-js@^2.4.1, core-js@^2.6.5:
+core-js@^2.4.0, core-js@^2.4.1:
   version "2.6.9"
   resolved "https://registry.yarnpkg.com/core-js/-/core-js-2.6.9.tgz#6b4b214620c834152e179323727fc19741b084f2"
   integrity sha512-HOpZf6eXmnl7la+cUdMnLvUxKNqLUzJvgIziQ0DiF3JwSImNphIqdGqzj6hIKyX04MmV0poclQ7+wjWvxQyR2A==
@@ -5063,6 +5062,11 @@ eslint-plugin-emotion@^10.0.14:
   resolved "https://registry.yarnpkg.com/eslint-plugin-emotion/-/eslint-plugin-emotion-10.0.14.tgz#c643ff2f34f85ae77a65b2056915e939cf7e8129"
   integrity sha512-kI0hTPA5oo7MAc2YcdF1JcT36TZ1Ci0S5sbA9aojZ3leEPyCH34YBB76/8NQ3/9gybqrekIEuEhr8MP6JZf95Q==
 
+eslint-plugin-es5@^1.4.1:
+  version "1.4.1"
+  resolved "https://registry.yarnpkg.com/eslint-plugin-es5/-/eslint-plugin-es5-1.4.1.tgz#258fe89bc5f72fbd9f5f7936c840151766821f1e"
+  integrity sha512-kktkmkF2O7pnSZYgrMiYMbt3wCKRIiXePwILv8USDG95YgP0PzhIxSIROLLKmiQQ/Z6LuhDGWTHK04gnbXBvkg==
+
 eslint-plugin-flowtype@^4.3.0:
   version "4.3.0"
   resolved "https://registry.yarnpkg.com/eslint-plugin-flowtype/-/eslint-plugin-flowtype-4.3.0.tgz#06d0837ac341caf369e7e6dbb112dd7fd21acf17"