Legacy String#at workaround

CHANGELOG.md

@@ -1,6 +1,6 @@
 ## Changelog
 ##### Unreleased
-- Nothing
+- Added a workaround of most cases breakage modern `String#at` after loading obsolete `String#at` proposal module, [#1019](https://github.com/zloirock/core-js/issues/1019)
 
 ##### 3.19.3 - 2021.12.06
 - Fixed internal slots check in methods of some built-in types, [#1017](https://github.com/zloirock/core-js/issues/1017)

packages/core-js/modules/es.string.at-alternative.js

@@ -9,7 +9,7 @@ var fails = require('../internals/fails');
 var charAt = uncurryThis(''.charAt);
 
 var FORCED = fails(function () {
-  return '𠮷'.at(0) !== '\uD842';
+  return '𠮷'.at(-2) !== '\uD842';
 });
 
 // `String.prototype.at` method

packages/core-js/modules/esnext.string.at.js

@@ -2,15 +2,22 @@
 var $ = require('../internals/export');
 var charAt = require('../internals/string-multibyte').charAt;
 var fails = require('../internals/fails');
+var requireObjectCoercible = require('../internals/require-object-coercible');
+var toIntegerOrInfinity = require('../internals/to-integer-or-infinity');
+var toString = require('../internals/to-string');
 
 var FORCED = fails(function () {
-  return '𠮷'.at(0) !== '𠮷';
+  return '𠮷'.at(-2) !== '𠮷';
 });
 
 // `String.prototype.at` method
 // https://github.com/mathiasbynens/String.prototype.at
 $({ target: 'String', proto: true, forced: FORCED }, {
-  at: function at(pos) {
-    return charAt(this, pos);
+  at: function at(index) {
+    var S = toString(requireObjectCoercible(this));
+    var len = S.length;
+    var relativeIndex = toIntegerOrInfinity(index);
+    var k = relativeIndex >= 0 ? relativeIndex : len + relativeIndex;
+    return (k < 0 || k >= len) ? undefined : charAt(S, k);
   }
 });

tests/compat/tests.js

@@ -889,7 +889,7 @@ GLOBAL.tests = {
       && set[Symbol.toStringTag];
   }],
   'es.string.at-alternative': function () {
-    return 'a'.at(-1) === 'a';
+    return '𠮷'.at(-2) === '\uD842';
   },
   'es.string.code-point-at': function () {
     return String.prototype.codePointAt;

tests/pure/es.string.at-alternative.js

@@ -1,10 +1,9 @@
-// TODO: disabled by default because of the conflict with another proposal
 import { STRICT } from '../helpers/constants';
 
 import at from 'core-js-pure/es/string/at';
 import Symbol from 'core-js-pure/es/symbol';
 
-QUnit.skip('String#at', assert => {
+QUnit.test('String#at', assert => {
   assert.isFunction(at);
   assert.same('1', at('123', 0));
   assert.same('2', at('123', 1));
@@ -20,7 +19,8 @@ QUnit.skip('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'));
+  // TODO: disabled by default because of the conflict with old proposal
+  // assert.same('\uD842', at('𠮷'));
   assert.same('1', at({ toString() { return '123'; } }, 0));
 
   assert.throws(() => at(Symbol(), 0), 'throws on symbol context');

tests/pure/esnext.string.at.js

@@ -5,16 +5,16 @@ import at from 'core-js-pure/features/string/at';
 QUnit.test('String#at', assert => {
   assert.isFunction(at);
   // String that starts with a BMP symbol
-  assert.same(at('abc\uD834\uDF06def', -Infinity), '');
-  assert.same(at('abc\uD834\uDF06def', -1), '');
+  // assert.same(at('abc\uD834\uDF06def', -Infinity), '');
+  // assert.same(at('abc\uD834\uDF06def', -1), '');
   assert.same(at('abc\uD834\uDF06def', -0), 'a');
   assert.same(at('abc\uD834\uDF06def', +0), 'a');
   assert.same(at('abc\uD834\uDF06def', 1), 'b');
   assert.same(at('abc\uD834\uDF06def', 3), '\uD834\uDF06');
   assert.same(at('abc\uD834\uDF06def', 4), '\uDF06');
   assert.same(at('abc\uD834\uDF06def', 5), 'd');
-  assert.same(at('abc\uD834\uDF06def', 42), '');
-  assert.same(at('abc\uD834\uDF06def', Infinity), '');
+  // assert.same(at('abc\uD834\uDF06def', 42), '');
+  // assert.same(at('abc\uD834\uDF06def', Infinity), '');
   assert.same(at('abc\uD834\uDF06def', null), 'a');
   assert.same(at('abc\uD834\uDF06def', undefined), 'a');
   assert.same(at('abc\uD834\uDF06def'), 'a');
@@ -28,18 +28,18 @@ QUnit.test('String#at', assert => {
   assert.same(at('abc\uD834\uDF06def', -0.9), 'a');
   assert.same(at('abc\uD834\uDF06def', 1.9), 'b');
   assert.same(at('abc\uD834\uDF06def', 7.9), 'f');
-  assert.same(at('abc\uD834\uDF06def', 2 ** 32), '');
+  // assert.same(at('abc\uD834\uDF06def', 2 ** 32), '');
   // String that starts with an astral symbol
-  assert.same(at('\uD834\uDF06def', -Infinity), '');
-  assert.same(at('\uD834\uDF06def', -1), '');
+  // assert.same(at('\uD834\uDF06def', -Infinity), '');
+  // assert.same(at('\uD834\uDF06def', -1), '');
   assert.same(at('\uD834\uDF06def', -0), '\uD834\uDF06');
   assert.same(at('\uD834\uDF06def', 0), '\uD834\uDF06');
   assert.same(at('\uD834\uDF06def', 1), '\uDF06');
   assert.same(at('\uD834\uDF06def', 2), 'd');
   assert.same(at('\uD834\uDF06def', 3), 'e');
   assert.same(at('\uD834\uDF06def', 4), 'f');
-  assert.same(at('\uD834\uDF06def', 42), '');
-  assert.same(at('\uD834\uDF06def', Infinity), '');
+  // assert.same(at('\uD834\uDF06def', 42), '');
+  // assert.same(at('\uD834\uDF06def', Infinity), '');
   assert.same(at('\uD834\uDF06def', null), '\uD834\uDF06');
   assert.same(at('\uD834\uDF06def', undefined), '\uD834\uDF06');
   assert.same(at('\uD834\uDF06def'), '\uD834\uDF06');
@@ -49,13 +49,13 @@ QUnit.test('String#at', assert => {
   assert.same(at('\uD834\uDF06def', '_'), '\uD834\uDF06');
   assert.same(at('\uD834\uDF06def', '1'), '\uDF06');
   // Lone high surrogates
-  assert.same(at('\uD834abc', -Infinity), '');
-  assert.same(at('\uD834abc', -1), '');
+  // assert.same(at('\uD834abc', -Infinity), '');
+  // assert.same(at('\uD834abc', -1), '');
   assert.same(at('\uD834abc', -0), '\uD834');
   assert.same(at('\uD834abc', 0), '\uD834');
   assert.same(at('\uD834abc', 1), 'a');
-  assert.same(at('\uD834abc', 42), '');
-  assert.same(at('\uD834abc', Infinity), '');
+  // assert.same(at('\uD834abc', 42), '');
+  // assert.same(at('\uD834abc', Infinity), '');
   assert.same(at('\uD834abc', null), '\uD834');
   assert.same(at('\uD834abc', undefined), '\uD834');
   assert.same(at('\uD834abc'), '\uD834');
@@ -65,13 +65,13 @@ QUnit.test('String#at', assert => {
   assert.same(at('\uD834abc', '_'), '\uD834');
   assert.same(at('\uD834abc', '1'), 'a');
   // Lone low surrogates
-  assert.same(at('\uDF06abc', -Infinity), '');
-  assert.same(at('\uDF06abc', -1), '');
+  // assert.same(at('\uDF06abc', -Infinity), '');
+  // assert.same(at('\uDF06abc', -1), '');
   assert.same(at('\uDF06abc', -0), '\uDF06');
   assert.same(at('\uDF06abc', 0), '\uDF06');
   assert.same(at('\uDF06abc', 1), 'a');
-  assert.same(at('\uDF06abc', 42), '');
-  assert.same(at('\uDF06abc', Infinity), '');
+  // assert.same(at('\uDF06abc', 42), '');
+  // assert.same(at('\uDF06abc', Infinity), '');
   assert.same(at('\uDF06abc', null), '\uDF06');
   assert.same(at('\uDF06abc', undefined), '\uDF06');
   assert.same(at('\uDF06abc'), '\uDF06');

tests/tests/es.string.at-alternative.js

@@ -1,7 +1,6 @@
-// TODO: disabled by default because of the conflict with another proposal
 import { STRICT } from '../helpers/constants';
 
-QUnit.skip('String#at', assert => {
+QUnit.test('String#at', assert => {
   const { at } = String.prototype;
   assert.isFunction(at);
   assert.arity(at, 1);
@@ -22,7 +21,8 @@ QUnit.skip('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());
+  // TODO: disabled by default because of the conflict with old proposal
+  // assert.same('\uD842', '𠮷'.at());
   assert.same('1', at.call({ toString() { return '123'; } }, 0));
 
   assert.throws(() => at.call(Symbol(), 0), 'throws on symbol context');

tests/tests/esnext.string.at.js

@@ -8,16 +8,16 @@ QUnit.test('String#at', assert => {
   assert.looksNative(at);
   assert.nonEnumerable(String.prototype, 'at');
   // String that starts with a BMP symbol
-  assert.same('abc\uD834\uDF06def'.at(-Infinity), '');
-  assert.same('abc\uD834\uDF06def'.at(-1), '');
+  // assert.same('abc\uD834\uDF06def'.at(-Infinity), '');
+  // assert.same('abc\uD834\uDF06def'.at(-1), '');
   assert.same('abc\uD834\uDF06def'.at(-0), 'a');
   assert.same('abc\uD834\uDF06def'.at(+0), 'a');
   assert.same('abc\uD834\uDF06def'.at(1), 'b');
   assert.same('abc\uD834\uDF06def'.at(3), '\uD834\uDF06');
   assert.same('abc\uD834\uDF06def'.at(4), '\uDF06');
   assert.same('abc\uD834\uDF06def'.at(5), 'd');
-  assert.same('abc\uD834\uDF06def'.at(42), '');
-  assert.same('abc\uD834\uDF06def'.at(Infinity), '');
+  // assert.same('abc\uD834\uDF06def'.at(42), '');
+  // assert.same('abc\uD834\uDF06def'.at(Infinity), '');
   assert.same('abc\uD834\uDF06def'.at(null), 'a');
   assert.same('abc\uD834\uDF06def'.at(undefined), 'a');
   assert.same('abc\uD834\uDF06def'.at(), 'a');
@@ -31,18 +31,18 @@ QUnit.test('String#at', assert => {
   assert.same('abc\uD834\uDF06def'.at(-0.9), 'a');
   assert.same('abc\uD834\uDF06def'.at(1.9), 'b');
   assert.same('abc\uD834\uDF06def'.at(7.9), 'f');
-  assert.same('abc\uD834\uDF06def'.at(2 ** 32), '');
+  // assert.same('abc\uD834\uDF06def'.at(2 ** 32), '');
   // String that starts with an astral symbol
-  assert.same('\uD834\uDF06def'.at(-Infinity), '');
-  assert.same('\uD834\uDF06def'.at(-1), '');
+  // assert.same('\uD834\uDF06def'.at(-Infinity), '');
+  // assert.same('\uD834\uDF06def'.at(-1), '');
   assert.same('\uD834\uDF06def'.at(-0), '\uD834\uDF06');
   assert.same('\uD834\uDF06def'.at(0), '\uD834\uDF06');
   assert.same('\uD834\uDF06def'.at(1), '\uDF06');
   assert.same('\uD834\uDF06def'.at(2), 'd');
   assert.same('\uD834\uDF06def'.at(3), 'e');
   assert.same('\uD834\uDF06def'.at(4), 'f');
-  assert.same('\uD834\uDF06def'.at(42), '');
-  assert.same('\uD834\uDF06def'.at(Infinity), '');
+  // assert.same('\uD834\uDF06def'.at(42), '');
+  // assert.same('\uD834\uDF06def'.at(Infinity), '');
   assert.same('\uD834\uDF06def'.at(null), '\uD834\uDF06');
   assert.same('\uD834\uDF06def'.at(undefined), '\uD834\uDF06');
   assert.same('\uD834\uDF06def'.at(), '\uD834\uDF06');
@@ -52,13 +52,13 @@ QUnit.test('String#at', assert => {
   assert.same('\uD834\uDF06def'.at('_'), '\uD834\uDF06');
   assert.same('\uD834\uDF06def'.at('1'), '\uDF06');
   // Lone high surrogates
-  assert.same('\uD834abc'.at(-Infinity), '');
-  assert.same('\uD834abc'.at(-1), '');
+  // assert.same('\uD834abc'.at(-Infinity), '');
+  // assert.same('\uD834abc'.at(-1), '');
   assert.same('\uD834abc'.at(-0), '\uD834');
   assert.same('\uD834abc'.at(0), '\uD834');
   assert.same('\uD834abc'.at(1), 'a');
-  assert.same('\uD834abc'.at(42), '');
-  assert.same('\uD834abc'.at(Infinity), '');
+  // assert.same('\uD834abc'.at(42), '');
+  // assert.same('\uD834abc'.at(Infinity), '');
   assert.same('\uD834abc'.at(null), '\uD834');
   assert.same('\uD834abc'.at(undefined), '\uD834');
   assert.same('\uD834abc'.at(), '\uD834');
@@ -68,13 +68,13 @@ QUnit.test('String#at', assert => {
   assert.same('\uD834abc'.at('_'), '\uD834');
   assert.same('\uD834abc'.at('1'), 'a');
   // Lone low surrogates
-  assert.same('\uDF06abc'.at(-Infinity), '');
-  assert.same('\uDF06abc'.at(-1), '');
+  // assert.same('\uDF06abc'.at(-Infinity), '');
+  // assert.same('\uDF06abc'.at(-1), '');
   assert.same('\uDF06abc'.at(-0), '\uDF06');
   assert.same('\uDF06abc'.at(0), '\uDF06');
   assert.same('\uDF06abc'.at(1), 'a');
-  assert.same('\uDF06abc'.at(42), '');
-  assert.same('\uDF06abc'.at(Infinity), '');
+  // assert.same('\uDF06abc'.at(42), '');
+  // assert.same('\uDF06abc'.at(Infinity), '');
   assert.same('\uDF06abc'.at(null), '\uDF06');
   assert.same('\uDF06abc'.at(undefined), '\uDF06');
   assert.same('\uDF06abc'.at(), '\uDF06');