Reduce dist size by 500 KB - reinstate browserslist, removing transforms for ancient browsers

[bradenmacdonald]

Description

Currently, Paragon is built using Babel's preset-env but without specifying any targets nor .browserslistrc config file. This has the unfortunate effect that:

When no targets are specified: Babel will assume you are targeting the oldest browsers possible. For example, @babel/preset-env will transform all ES2015-ES2020 code to be ES5 compatible.

We recognize this isn’t ideal and will be revisiting this in Babel v8.

We recommend setting targets to reduce the output code size.

So if you look at any of the files in dist/, you'll see that they are being transformed in an extremely inefficient way in order to support pre-ES5 browsers (that are more than a decade old!).

In this PR, I am proposing we change the build to use the recommended targets: defaults option. This small change to the config results in a big 500KB savings to the transformed files in dist when npm run build is run:

Before: 2,919,906 bytes (4.5 MB on disk) for 740 items
After: 2,401,170 bytes (4.1 MB on disk) for 740 items

I have also removed @babel/plugin-proposal-class-properties and @babel/plugin-proposal-object-rest-spread because they're both deprecated (click their links for details), and the replacements are now included in preset-env so don't need to be separately installed.

See also #3283 which makes a similar change for the icons.

What about compatibility?

This is now using the browserslist defaults query which is equivalent to > 0.5%, last 2 versions, Firefox ESR, not dead. This is considered best practice. We could change it to @edx/browserslist-config but as far as I can tell that's actually less compatible than the browserslist defaults (because it explicitly specifies only the few browsers supported by Open edX, whereas the browserslist defaults includes old browsers if they have enough marketshare). As an example, they advise "Don’t remove browsers just because you don’t know them. Opera Mini has 100 million users in Africa and it is more popular in the global market than Microsoft Edge. Chinese QQ Browsers has more market share than Firefox and desktop Safari combined." but Open edX browserslist config has removed those browsers.

Example

Here is a typical diff showing the simplification that results in the build. This is dist/Alert/index.js.

@@ -1,20 +1,3 @@
-// dist/Alert/index.js
-function _typeof(o) { "@babel/helpers - typeof"; return _typeof = "function" == typeof Symbol && "symbol" == typeof Symbol.iterator ? function (o) { return typeof o; } : function (o) { return o && "function" == typeof Symbol && o.constructor === Symbol && o !== Symbol.prototype ? "symbol" : typeof o; }, _typeof(o); }
-var _excluded = ["children", "icon", "actions", "dismissible", "onClose", "closeLabel", "stacked"];
-function ownKeys(e, r) { var t = Object.keys(e); if (Object.getOwnPropertySymbols) { var o = Object.getOwnPropertySymbols(e); r && (o = o.filter(function (r) { return Object.getOwnPropertyDescriptor(e, r).enumerable; })), t.push.apply(t, o); } return t; }
-function _objectSpread(e) { for (var r = 1; r < arguments.length; r++) { var t = null != arguments[r] ? arguments[r] : {}; r % 2 ? ownKeys(Object(t), !0).forEach(function (r) { _defineProperty(e, r, t[r]); }) : Object.getOwnPropertyDescriptors ? Object.defineProperties(e, Object.getOwnPropertyDescriptors(t)) : ownKeys(Object(t)).forEach(function (r) { Object.defineProperty(e, r, Object.getOwnPropertyDescriptor(t, r)); }); } return e; }
-function _defineProperty(obj, key, value) { key = _toPropertyKey(key); if (key in obj) { Object.defineProperty(obj, key, { value: value, enumerable: true, configurable: true, writable: true }); } else { obj[key] = value; } return obj; }
-function _toPropertyKey(t) { var i = _toPrimitive(t, "string"); return "symbol" == _typeof(i) ? i : i + ""; }
-function _toPrimitive(t, r) { if ("object" != _typeof(t) || !t) return t; var e = t[Symbol.toPrimitive]; if (void 0 !== e) { var i = e.call(t, r || "default"); if ("object" != _typeof(i)) return i; throw new TypeError("@@toPrimitive must return a primitive value."); } return ("string" === r ? String : Number)(t); }
-function _extends() { _extends = Object.assign ? Object.assign.bind() : function (target) { for (var i = 1; i < arguments.length; i++) { var source = arguments[i]; for (var key in source) { if (Object.prototype.hasOwnProperty.call(source, key)) { target[key] = source[key]; } } } return target; }; return _extends.apply(this, arguments); }
-function _slicedToArray(arr, i) { return _arrayWithHoles(arr) || _iterableToArrayLimit(arr, i) || _unsupportedIterableToArray(arr, i) || _nonIterableRest(); }
-function _nonIterableRest() { throw new TypeError("Invalid attempt to destructure non-iterable instance.\nIn order to be iterable, non-array objects must have a [Symbol.iterator]() method."); }
-function _unsupportedIterableToArray(o, minLen) { if (!o) return; if (typeof o === "string") return _arrayLikeToArray(o, minLen); var n = Object.prototype.toString.call(o).slice(8, -1); if (n === "Object" && o.constructor) n = o.constructor.name; if (n === "Map" || n === "Set") return Array.from(o); if (n === "Arguments" || /^(?:Ui|I)nt(?:8|16|32)(?:Clamped)?Array$/.test(n)) return _arrayLikeToArray(o, minLen); }
-function _arrayLikeToArray(arr, len) { if (len == null || len > arr.length) len = arr.length; for (var i = 0, arr2 = new Array(len); i < len; i++) arr2[i] = arr[i]; return arr2; }
-function _iterableToArrayLimit(r, l) { var t = null == r ? null : "undefined" != typeof Symbol && r[Symbol.iterator] || r["@@iterator"]; if (null != t) { var e, n, i, u, a = [], f = !0, o = !1; try { if (i = (t = t.call(r)).next, 0 === l) { if (Object(t) !== t) return; f = !1; } else for (; !(f = (e = i.call(t)).done) && (a.push(e.value), a.length !== l); f = !0); } catch (r) { o = !0, n = r; } finally { try { if (!f && null != t["return"] && (u = t["return"](), Object(u) !== u)) return; } finally { if (o) throw n; } } return a; } }
-function _arrayWithHoles(arr) { if (Array.isArray(arr)) return arr; }
-function _objectWithoutProperties(source, excluded) { if (source == null) return {}; var target = _objectWithoutPropertiesLoose(source, excluded); var key, i; if (Object.getOwnPropertySymbols) { var sourceSymbolKeys = Object.getOwnPropertySymbols(source); for (i = 0; i < sourceSymbolKeys.length; i++) { key = sourceSymbolKeys[i]; if (excluded.indexOf(key) >= 0) continue; if (!Object.prototype.propertyIsEnumerable.call(source, key)) continue; target[key] = source[key]; } } return target; }
-function _objectWithoutPropertiesLoose(source, excluded) { if (source == null) return {}; var target = {}; var sourceKeys = Object.keys(source); var key, i; for (i = 0; i < sourceKeys.length; i++) { key = sourceKeys[i]; if (excluded.indexOf(key) >= 0) continue; target[key] = source[key]; } return target; }
 import React, { useCallback, useEffect, useState } from 'react';
 import PropTypes from 'prop-types';
 import classNames from 'classnames';
@@ -26,42 +9,42 @@
 import breakpoints from '../utils/breakpoints';
 import Button from '../Button';
 import ActionRow from '../ActionRow';
-export var ALERT_CLOSE_LABEL_TEXT = 'Dismiss';
-var Alert = /*#__PURE__*/React.forwardRef(function (_ref, ref) {
-  var children = _ref.children,
-    icon = _ref.icon,
-    actions = _ref.actions,
-    dismissible = _ref.dismissible,
-    onClose = _ref.onClose,
-    closeLabel = _ref.closeLabel,
-    stacked = _ref.stacked,
-    props = _objectWithoutProperties(_ref, _excluded);
-  var _useState = useState(stacked),
-    _useState2 = _slicedToArray(_useState, 2),
-    isStacked = _useState2[0],
-    setIsStacked = _useState2[1];
-  var isExtraSmall = useMediaQuery({
+export const ALERT_CLOSE_LABEL_TEXT = 'Dismiss';
+const Alert = /*#__PURE__*/React.forwardRef((_ref, ref) => {
+  let {
+    children,
+    icon,
+    actions,
+    dismissible,
+    onClose,
+    closeLabel,
+    stacked,
+    ...props
+  } = _ref;
+  const [isStacked, setIsStacked] = useState(stacked);
+  const isExtraSmall = useMediaQuery({
     maxWidth: breakpoints.extraSmall.maxWidth
   });
-  var actionButtonSize = 'sm';
-  useEffect(function () {
+  const actionButtonSize = 'sm';
+  useEffect(() => {
     if (isExtraSmall) {
       setIsStacked(true);
     } else {
       setIsStacked(stacked);
     }
   }, [isExtraSmall, stacked]);
-  var cloneActionElement = useCallback(function (Action) {
-    var addtlActionProps = {
+  const cloneActionElement = useCallback(Action => {
+    const addtlActionProps = {
       size: actionButtonSize,
       key: Action.props.children
     };
     return /*#__PURE__*/React.cloneElement(Action, addtlActionProps);
   }, []);
-  return /*#__PURE__*/React.createElement(BaseAlert, _extends({}, props, {
+  return /*#__PURE__*/React.createElement(BaseAlert, {
+    ...props,
     className: classNames('alert-content', props.className),
     ref: ref
-  }), icon && /*#__PURE__*/React.createElement(Icon, {
+  }, icon && /*#__PURE__*/React.createElement(Icon, {
     src: icon,
     className: "alert-icon"
   }), /*#__PURE__*/React.createElement("div", {
@@ -71,7 +54,7 @@
     })
   }, /*#__PURE__*/React.createElement("div", {
     className: "alert-message-content"
-  }, children), (dismissible || (actions === null || actions === void 0 ? void 0 : actions.length) > 0) && /*#__PURE__*/React.createElement(ActionRow, {
+  }, children), (dismissible || actions?.length > 0) && /*#__PURE__*/React.createElement(ActionRow, {
     className: "pgn__alert-actions"
   }, /*#__PURE__*/React.createElement(ActionRow.Spacer, null), dismissible && /*#__PURE__*/React.createElement(Button, {
     size: actionButtonSize,
@@ -87,15 +70,19 @@
 // This is needed to display a default prop for Alert.Heading element
 // Copied from react-bootstrap since BaseAlert.Heading component doesn't have defaultProps,
 // so there seems to be no other way of providing correct default prop for base element
-var DivStyledAsH4 = divWithClassName('h4');
+const DivStyledAsH4 = divWithClassName('h4');
 DivStyledAsH4.displayName = 'DivStyledAsH4';
 function AlertHeading(props) {
-  return /*#__PURE__*/React.createElement(BaseAlert.Heading, props);
+  return /*#__PURE__*/React.createElement(BaseAlert.Heading, {
+    ...props
+  });
 }
 function AlertLink(props) {
-  return /*#__PURE__*/React.createElement(BaseAlert.Link, props);
+  return /*#__PURE__*/React.createElement(BaseAlert.Link, {
+    ...props
+  });
 }
-var commonPropTypes = {
+const commonPropTypes = {
   /** Specifies the base element */
   as: PropTypes.elementType,
   /** Overrides underlying component base CSS class name */
@@ -111,7 +98,8 @@
   as: DivStyledAsH4,
   bsPrefix: 'alert-heading'
 };
-Alert.propTypes = _objectSpread(_objectSpread({}, BaseAlert.propTypes), {}, {
+Alert.propTypes = {
+  ...BaseAlert.propTypes,
   /** Specifies class name to append to the base element */
   className: PropTypes.string,
   /** Overrides underlying component base CSS class name */
@@ -123,7 +111,7 @@
    * more detailed customization is also provided.
    */
   transition: PropTypes.oneOfType([PropTypes.bool, PropTypes.shape({
-    "in": PropTypes.bool,
+    in: PropTypes.bool,
     appear: PropTypes.bool,
     children: PropTypes.node,
     onEnter: PropTypes.func,
@@ -149,17 +137,18 @@
   stacked: PropTypes.bool,
   /** Sets the text for alert close button, defaults to 'Dismiss'. */
   closeLabel: PropTypes.oneOfType([PropTypes.string, PropTypes.element])
-});
-Alert.defaultProps = _objectSpread(_objectSpread({}, BaseAlert.defaultProps), {}, {
+};
+Alert.defaultProps = {
+  ...BaseAlert.defaultProps,
   children: undefined,
   icon: undefined,
   actions: undefined,
   dismissible: false,
-  onClose: function onClose() {},
+  onClose: () => {},
   closeLabel: undefined,
   show: true,
   stacked: false
-});
+};
 Alert.Heading = AlertHeading;
 Alert.Link = AlertLink;
 export default Alert;

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 93.31%. Comparing base (fc888d5) to head (f0cb655).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #3284   +/-   ##
=======================================
  Coverage   93.31%   93.31%           
=======================================
  Files         249      249           
  Lines        4441     4441           
  Branches     1014     1014           
=======================================
  Hits         4144     4144           
  Misses        294      294           
  Partials        3        3           

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[brian-smith-tcril]

After discussing in Paragon working group today we decided it likely makes the most sense to bring back the https://github.com/openedx/browserslist-config/ dependency and update that repo to follow browserslist best practices. That repo is currently set to past 2 major versions to match what was communicated on the edx.org support page, but it absolutely makes sense to increase the coverage to follow best practices. This will ensure we have the same level of support throughout all applications instead of just in Paragon.

[bradenmacdonald]

Ah, I wasn't aware that it had been removed at some point: #2501

That issue says

browserslist should only be defined in MFEs or any regular applications that render pages on the website, not in component libraries like Paragon.

But this is only true if we distribute Paragon in a "buildless" manner, as .tsx/.jsx source files. As far as I know, none of our MFEs consume Paragon in that way. Since we do have an npm run build step and we are using Babel to transform Paragon files from .jsx/.tsx to .js, the config does matter, and right now it is using a bad default.

It would also be reasonable to distribute Paragon in the most modern form possible, and rely on MFE bunders (webpack+babel) to apply compatibility transforms/shims later where needed. But distributing it in the most compatible form (supporting ancient browsers) forces all the compatibility shims into each and every file, and as far as I know they can't get removed by later steps of the bundling process (in MFEs).

After discussing in Paragon working group today we decided it likely makes the most sense to bring back the https://github.com/openedx/browserslist-config/ dependency and update that repo to follow browserslist best practices. That repo is currently set to past 2 major versions to match what was communicated on the edx.org support page, but it absolutely makes sense to increase the coverage to follow best practices. This will ensure we have the same level of support throughout all applications instead of just in Paragon.

Sounds like a good plan! Do you want me to update this PR to add that dependency?

[brian-smith-tcril]

Sounds like a good plan! Do you want me to update this PR to add that dependency?

That would be wonderful! Just adding back the dependency won't quite cover everything though, so a PR to https://github.com/openedx/browserslist-config updating the exports to use browserslist defaults would be great too!