Implement Array.prototype.at

quickjs.c

@@ -38412,6 +38412,38 @@ static int JS_isConcatSpreadable(JSContext *ctx, JSValueConst obj)
     return JS_IsArray(ctx, obj);
 }
 
+static JSValue js_array_at(JSContext *ctx, JSValueConst this_val,
+                           int argc, JSValueConst *argv)
+{
+    JSValue obj, ret;
+    int64_t len, idx;
+    JSValue *arrp;
+    uint32_t count;
+
+    ret = JS_EXCEPTION;
+    obj = JS_ToObject(ctx, this_val);
+    if (js_get_length64(ctx, &len, obj))
+        goto exception;
+
+    if (JS_ToInt64Sat(ctx, &idx, argv[0]))
+        goto exception;
+
+    if (idx < 0)
+        idx = len + idx;
+
+    if (idx < 0 || idx >= len) {
+        ret = JS_UNDEFINED;
+    } else if (js_get_fast_array(ctx, obj, &arrp, &count) && count == len) {
+        ret = JS_DupValue(ctx, arrp[idx]);
+    } else if (!JS_TryGetPropertyInt64(ctx, obj, idx, &ret)) {
+        ret = JS_UNDEFINED;
+    }
+
+ exception:
+    JS_FreeValue(ctx, obj);
+    return ret;
+}
+
 static JSValue js_array_concat(JSContext *ctx, JSValueConst this_val,
                                int argc, JSValueConst *argv)
 {
@@ -39773,6 +39805,7 @@ static const JSCFunctionListEntry js_iterator_proto_funcs[] = {
 };
 
 static const JSCFunctionListEntry js_array_proto_funcs[] = {
+    JS_CFUNC_DEF("at", 1, js_array_at ),
     JS_CFUNC_DEF("concat", 1, js_array_concat ),
     JS_CFUNC_MAGIC_DEF("every", 1, js_array_every, special_every ),
     JS_CFUNC_MAGIC_DEF("some", 1, js_array_every, special_some ),

test262.conf

@@ -58,7 +58,7 @@ arbitrary-module-namespace-names=skip
 array-find-from-last=skip
 array-grouping=skip
 Array.fromAsync=skip
-Array.prototype.at=skip
+Array.prototype.at
 Array.prototype.flat
 Array.prototype.flatMap
 Array.prototype.flatten