Deduplicate an array with one Set

My list of signup emails has duplicates.

BeginnerRead 2 minDoing: 15 minutes5 steps

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What you'll have at the end

A one-line function that returns the array with every duplicate removed

Before you start

You need

an array already holding every signup entry you want deduplicated, whether that's plain email strings or the raw records they came from

Not covered

catching two different addresses that are really one mistake, like a typo (proto@gnail.com instead of proto@gmail.com), which needs comparison logic well beyond an exact-value check

Leans on

JavaScript Cheat Sheetthe Set, spread, and object-equality rules this recipe builds on all live in one table there
Frontend Development Cheat Sheetshows exactly what the browser's own email input checks, and doesn't check, before your code ever runs

Get every entry down to one comparable string

Flatten records to a list of emails
Normalize casing and whitespace first

Deduplicate it and prove the count dropped

Build the Set and spread it back
Confirm the duplicates are actually gone

Package it as a function you can reuse

Package it as a reusable function

Checked 21 Aug 2026

Part of the JavaScript cookbook