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javascriptarrayscompare

Checking for duplicate strings in JavaScript array

I have JS array with strings, for example:

var strArray = [ "q", "w", "w", "e", "i", "u", "r"];

I need to compare for duplicate strings inside array, and if duplicate string exists, there should be alert box pointing to that string.

I was trying to compare it with for loop, but I don't know how to write code so that array checks its own strings for duplicates, without already pre-determined string to compare.

Solution

  • The findDuplicates function (below) compares index of all items in array with index of first occurrence of same item. If indexes are not same returns it as duplicate.

    let strArray = [ "q", "w", "w", "w", "e", "i", "i", "u", "r"];
let findDuplicates = arr => arr.filter((item, index) => arr.indexOf(item) !== index)

console.log(findDuplicates(strArray)) // All duplicates
console.log([...new Set(findDuplicates(strArray))]) // Unique duplicates