JSFiddle - React, Tailwind, and code Playground

JavaScript

var arr1 = [0,0,0,1,2,3,4,3,2,3,4,3,4,3,5];
var arr2 = [];

for (var i = 0; i < arr1.length; i++) {
   if (arr2[arr1[i]] != undefined)
       arr2[arr1[i]]++;
   else
       arr2[arr1[i]] = 1;
}

console.log(arr2);