Algorithms and Data Structures · Middle · Question 66 of 75

Why does the order of keys in a JavaScript object not always match insertion order?

Object.keys({ b: 1, 2: 1, a: 1, 1: 1 });

1Keys are always sorted alphabetically by the engine
2The order is random and may change between runs
✓Correct answer: Integer-like keys go first in ascending order, then the rest

Explanation

The result is ["1", "2", "b", "a"]. If you need a dictionary with predictable insertion order for any keys, use Map.

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Why does the order of keys in a JavaScript object not always match… - Algorithms and Data Structures Middle interview question