add code points / code units explicit feature detection for String#at

zloirock · Nov 24, 2020 · 9c07cee · 9c07cee
1 parent 1b27991
commit 9c07cee
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Showing 6 changed files with 16 additions and 3 deletions.
diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -11,6 +11,7 @@
   - `%TypedArray%#filterOut`
 - Added [array deduplication stage 1 proposal](https://github.com/tc39/proposal-array-unique)
   - `Array#uniqueBy`
+- Added code points / code units explicit feature detection in `String#at` for preventing breakage code which use obsolete `String#at` proposal polyfill
 - Added the missed `(es|stable)/instance/replace-all` entries
 - Updated compat data mapping for Opera - from Opera 69, the difference with Chrome versions increased to 14
 - Compat data mapping for modern Android WebView to Chrome moved from targets parser directly to compat data

diff --git a/packages/core-js/modules/esnext.string.at-alternative.js b/packages/core-js/modules/esnext.string.at-alternative.js
@@ -4,10 +4,15 @@ var $ = require('../internals/export');
 var requireObjectCoercible = require('../internals/require-object-coercible');
 var toLength = require('../internals/to-length');
 var toInteger = require('../internals/to-integer');
+var fails = require('../internals/fails');
+
+var FORCED = fails(function () {
+  return '𠮷'.at(0) !== '\uD842';
+});
 
 // `String.prototype.at` method
 // https://github.com/tc39/proposal-relative-indexing-method
-$({ target: 'String', proto: true }, {
+$({ target: 'String', proto: true, forced: FORCED }, {
   at: function at(index) {
     var S = String(requireObjectCoercible(this));
     var len = toLength(S.length);

diff --git a/packages/core-js/modules/esnext.string.at.js b/packages/core-js/modules/esnext.string.at.js
@@ -1,10 +1,15 @@
 'use strict';
 var $ = require('../internals/export');
 var charAt = require('../internals/string-multibyte').charAt;
+var fails = require('../internals/fails');
+
+var FORCED = fails(function () {
+  return '𠮷'.at(0) !== '𠮷';
+});
 
 // `String.prototype.at` method
 // https://github.com/mathiasbynens/String.prototype.at
-$({ target: 'String', proto: true }, {
+$({ target: 'String', proto: true, forced: FORCED }, {
   at: function at(pos) {
     return charAt(this, pos);
   }

diff --git a/tests/compat/tests.js b/tests/compat/tests.js
@@ -1425,7 +1425,7 @@ GLOBAL.tests = {
     return Set.prototype.union;
   },
   'esnext.string.at': function () {
-    return String.prototype.at;
+    return '𠮷'.at(0) === '𠮷';
   },
   'esnext.string.code-points': function () {
     return String.prototype.codePoints;

diff --git a/tests/pure/esnext.string.at-alternative.js b/tests/pure/esnext.string.at-alternative.js
@@ -19,6 +19,7 @@ QUnit.test('String#at', assert => {
   assert.same('1', at('1', NaN));
   assert.same('1', at('1'));
   assert.same('1', at('123', -0));
+  assert.same('\uD842', at('𠮷'));
   assert.same('1', at({ toString() { return '123'; } }, 0));
   if (STRICT) {
     assert.throws(() => at(null, 0), TypeError);

diff --git a/tests/tests/esnext.string.at-alternative.js b/tests/tests/esnext.string.at-alternative.js
@@ -22,6 +22,7 @@ QUnit.test('String#at', assert => {
   assert.same('1', '1'.at(NaN));
   assert.same('1', '1'.at());
   assert.same('1', '123'.at(-0));
+  assert.same('\uD842', '𠮷'.at());
   assert.same('1', at.call({ toString() { return '123'; } }, 0));
   if (STRICT) {
     assert.throws(() => at.call(null, 0), TypeError);