Transform .at to property access to improve performance (#14590)

Co-authored-by: fisker Cheung <lionkay@gmail.com>

scripts/build/shims/at.js

@@ -10,9 +10,14 @@ const at = (isOptionalObject, object, index) => {
     return;
   }
 
-  return object.at
-    ? object.at(index)
-    : object[index < 0 ? object.length + index : index];
+  // "relative indexing" is not available in Node.js v14
+  // `.at` method is slower than property access on Node.js v16 and v18, see #14396
+  // Only checked arrays and strings, since we haven't use `TypedArray`, and the transform only works for sources
+  if (Array.isArray(object) || typeof object === "string") {
+    return object[index < 0 ? object.length + index : index];
+  }
+
+  return object.at(index);
 };
 
 export default at;

src/common/ast-path.js

@@ -16,8 +16,7 @@ class AstPath {
 
   /** @type {object} */
   get node() {
-    // eslint-disable-next-line unicorn/prefer-at -- `Array#at` is slow on Node.js v16 and v18
-    return this.stack[this.stack.length - 1];
+    return this.stack.at(-1);
   }
 
   /** @type {object | null} */