js find dublicate value code example
Example 1: how to get duplicate values from array in javascript
let a = [1, 2, 3, 4, 2, 2, 4, 1, 5, 6]
let b = [...new Set(a.sort().filter((o, i) => o !== undefined && a[i + 1] !== undefined && o === a[i + 1]))]
Example 2: how to get duplicate values from array in javascript
const names = ['Mike', 'Matt', 'Nancy', 'Adam', 'Jenny', 'Nancy', 'Carl']
const count = names =>
names.reduce((a, b) => ({ ...a,
[b]: (a[b] || 0) + 1
}), {})
const duplicates = dict =>
Object.keys(dict).filter((a) => dict[a] > 1)
console.log(count(names))
console.log(duplicates(count(names)))