JSFiddle - React, Tailwind, and code Playground

JavaScript

var arr = ['ab','pq','mn','ab','mn','ab'];
var obj = { };
for (var i = 0, j = arr.length; i < j; i++) {
   if (obj[arr[i]]) {
      obj[arr[i]]++;
   }
   else {
      obj[arr[i]] = 1;
   } 
}

console.log(obj);