ScriptdrillRemove duplicates by a field
A JavaScript exercise from Scriptdrill. Solve it with a code editor in your browser that runs your function against example and hidden tests, and it is checked the moment you submit.
The task
Return the items with duplicates removed, where two items are duplicates when `item[key]` is the same value. Keep the first item for each value, in the original order. Values are compared the way a `Set` compares them, so the number `1` and the string `"1"` are different.
What this exercise teaches
A Set remembers values with their type, so 1 and "1" stay apart, which a plain object used as a lookup would merge. Checking before adding keeps the first occurrence.
A hint if you get stuck
Keep a `Set` of the values you have seen and `filter` the items: keep an item only when its value is not in the set yet.
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