Get all non-unique values (i.e.: duplicate/more than one occurrence) in an array

Question

I need to check a JavaScript array to see if there are any duplicate values. What\'s the easiest way to do this? I just need to find what the duplicated values are - I don\'

Answer 1

Shortest vanilla JS:

[1,1,2,2,2,3].filter((v,i,a) => a.indexOf(v) !== i) // [1, 2, 2]