src/builtins/array-at.tq

// Copyright 2020 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

namespace array {
// https://tc39.es/proposal-item-method/#sec-array.prototype.at
transitioning javascript builtin ArrayPrototypeAt(
    js-implicit context: NativeContext, receiver: JSAny)(index: JSAny): JSAny {
  // 1. Let O be ? ToObject(this value).
  const o = ToObject_Inline(context, receiver);
  // 2. Let len be ? LengthOfArrayLike(O).
  const len = GetLengthProperty(o);
  // 3. Let relativeIndex be ? ToInteger(index).
  const relativeIndex = ToInteger_Inline(index);
  // 4. If relativeIndex ≥ 0, then
  //   a. Let k be relativeIndex.
  // 5. Else,
  //   a. Let k be len + relativeIndex.
  const k = relativeIndex >= 0 ? relativeIndex : len + relativeIndex;
  // 6. If k < 0 or k ≥ len, then return undefined.
  if (k < 0 || k >= len) {
    return Undefined;
  }
  // 7. Return ? Get(O, ! ToString(k)).
  return GetProperty(o, k);
}
}