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// 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 {
macro ConvertRelativeIndex(index: Number, length: Number):
Number labels OutOfBoundsLow, OutOfBoundsHigh {
const relativeIndex = index >= 0 ? index : length + index;
if (relativeIndex < 0) goto OutOfBoundsLow;
if (relativeIndex >= length) goto OutOfBoundsHigh;
return relativeIndex;
}
// 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);
try {
// 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 = ConvertRelativeIndex(relativeIndex, len) otherwise OutOfBounds,
OutOfBounds;
// 7. Return ? Get(O, ! ToString(k)).
return GetProperty(o, k);
} label OutOfBounds {
// 6. If k < 0 or k ≥ len, then return undefined.
return Undefined;
}
}
}
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