Add a quirk for Array.at

Trivial to polyfill, needed by various pages in the wild,
and only natively available with Qt 6.2.

Closes #7501
Also see #7237 and 726d5e614b1f80c339084eba7d1c240bf467fa9b

(cherry picked from commit ce64e5d899666bd469bf07bd0fecbc75d4bfed3a)

4 files changed, 70 insertions, 2 deletions

diff --git a/qutebrowser/browser/webengine/webenginetab.py b/qutebrowser/browser/webengine/webenginetab.py
index 5c5d9ccfc..3ff1547d3 100644
--- a/qutebrowser/browser/webengine/webenginetab.py
+++ b/qutebrowser/browser/webengine/webenginetab.py
@@ -1211,7 +1211,11 @@ class _WebEngineScripts(QObject):
             _Quirk(
                 'object_fromentries',
                 predicate=versions.webengine < utils.VersionNumber(5, 13),
-            )
+            ),
+            _Quirk(
+                'array_at',
+                predicate=versions.webengine < utils.VersionNumber(6, 2),
+            ),
         ]
 
         for quirk in quirks:
diff --git a/qutebrowser/javascript/.eslintrc.yaml b/qutebrowser/javascript/.eslintrc.yaml
index 43fd1b6e6..566304c27 100644
--- a/qutebrowser/javascript/.eslintrc.yaml
+++ b/qutebrowser/javascript/.eslintrc.yaml
@@ -29,7 +29,7 @@ rules:
     init-declarations: "off"
     no-plusplus: "off"
     no-extra-parens: "off"
-    id-length: ["error", {"exceptions": ["i", "k", "v", "x", "y"]}]
+    id-length: ["error", {"exceptions": ["i", "n", "k", "v", "x", "y"]}]
     object-shorthand: "off"
     max-statements: ["error", {"max": 40}]
     quotes: ["error", "double", {"avoidEscape": true}]
diff --git a/qutebrowser/javascript/quirks/array_at.user.js b/qutebrowser/javascript/quirks/array_at.user.js
new file mode 100644
index 000000000..0badebd77
--- /dev/null
+++ b/qutebrowser/javascript/quirks/array_at.user.js
@@ -0,0 +1,58 @@
+// Based on: https://github.com/tc39/proposal-relative-indexing-method#polyfill
+
+/*
+Copyright (c) 2020 Tab Atkins Jr.
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.
+*/
+
+/* eslint-disable no-invalid-this */
+
+"use strict";
+
+(function() {
+    function at(idx) {
+        // ToInteger() abstract op
+        let n = Math.trunc(idx) || 0;
+        // Allow negative indexing from the end
+        if (n < 0) {
+            n += this.length;
+        }
+        // OOB access is guaranteed to return undefined
+        if (n < 0 || n >= this.length) {
+            return undefined;
+        }
+        // Otherwise, this is just normal property access
+        return this[n];
+    }
+
+    const TypedArray = Reflect.getPrototypeOf(Int8Array);
+    for (const type of [Array, String, TypedArray]) {
+        Object.defineProperty(
+            type.prototype,
+            "at",
+            {
+                "value": at,
+                "writable": true,
+                "enumerable": false,
+                "configurable": true,
+            }
+        );
+    }
+})();
diff --git a/tests/unit/javascript/test_js_quirks.py b/tests/unit/javascript/test_js_quirks.py
index 52b9a090f..35ce37f16 100644
--- a/tests/unit/javascript/test_js_quirks.py
+++ b/tests/unit/javascript/test_js_quirks.py
@@ -61,6 +61,12 @@ from qutebrowser.utils import usertypes
         {'0': 'a', '1': 'b'},
         id='object-fromentries',
     ),
+    pytest.param(
+        QUrl("https://test.qutebrowser.org/linkedin"),
+        '[1, 2, 3].at(1)',
+        2,
+        id='array-at',
+    ),
 ])
 def test_js_quirks(config_stub, js_tester_webengine, base_url, source, expected):
     config_stub.val.content.site_specific_quirks.skip = []