Checking for duplicate strings in JavaScript array
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", "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 duplicatesUsing ES6 features
- Because each value in the Set has to be unique, the value equality will be checked.
function checkIfDuplicateExists(arr) {
return new Set(arr).size !== arr.length
}
var arr = ["a", "a", "b", "c"];
var arr1 = ["a", "b", "c"];
console.log(checkIfDuplicateExists(arr)); // true
console.log(checkIfDuplicateExists(arr1)); // false