JSFiddle - React, Tailwind, and code Playground

JavaScript

var arr = ['ab','pq','mn','ab','mn','ab'];

occurrences = arr.reduce(function(occ, item) {
  occ[item] = (occ[item] || 0) + 1;
  return occ;
}, {});

console.log(occurrences);        // {ab: 3, pq: 1, mn: 2}
console.log(occurrences['mn']);  // 2