Travail personnel : reduce !

Prérequis

reduce 1
reduce 2
reduce 3
reduce 4
reduce 5

En action : 

const words = [10,2,2,1,10,10,10,10,10];

const o = words.reduce((a, x) => {

   if (!a[x]) a[x] = 0;

   a[x]=a[x]+1;

return a},{});

code