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Discussion on: JavaScript: How to Check if an Array has Duplicate Values

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igorfilippov3 profile image
Ihor Filippov • • Edited

Nice technique. But it works only with primitives.
If you do not mind I want to add a bit more info about this topic.
If you need to find duplicates in array of objects, you can do something like this:

function checkForDuplicates(source, keyName) {
  return source.filter((item, index, array) => {
    return array.findIndex(t => t[keyName] === item[keyName]) === index;
  }).length !== source.length
}
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johandalabacka profile image
Johan Dahl • • Edited

or use almost the same technique as the author:

function checkForDuplicates(array, keyName) {
  return new Set(array.map(item => item[keyName])).size !== array.length
}
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igorfilippov3 profile image
Ihor Filippov •

Yep. It is cleaner than mine.

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mohammedelseddik profile image
MohammedElseddik •

could you please explain this syntax to me and thank you in advance.