Is the complexity of Object.entries() in JavaScript known? According to information from this question, it seems like it could possibly be O(n) if implemented by collecting keys and values as arrays and then combining them together?
Is the complexity of Object.entries() in JavaScript known? According to information from this question, it seems like it could possibly be O(n) if implemented by collecting keys and values as arrays and then combining them together?
(Expert in V8 development speaking.)
To put it simply, yes, the time complexity of Object.entries() is typically O(n).
However, for large objects with thousands of properties, the complexity becomes O(n log n). This is due to the fact that we store properties of large objects (as well as certain "complex" small objects) in a dictionary. Retrieving all keys from this dictionary has O(n) complexity, but because Object.entries() is intended to return entries in property creation order, we must sort them, which results in an O(n log n) operation.
(This also applies to Object.keys(); the mentioned question/response is inaccurate regarding this aspect.)
Additionally, each entry requires allocation of an array, causing Object.entries() to produce significant garbage when used on large objects. Despite this, the complexity remains unchanged.
One important factor to consider is that calling a getter for a property's value can have unpredictable outcomes. The getter function has the potential to execute any kind of logic, making it impossible to determine the performance:
var o = {};
Object.defineProperty(o, "there's nothing O(n) about this",
{get: () => { while (true); }, enumerable: true});
console.log(Object.entries(o));
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