migratory_birds.js

// boiler plate for js 
'use strict';

const fs = require('fs');

process.stdin.resume();
process.stdin.setEncoding('utf-8');

let inputString = '';
let currentLine = 0;

process.stdin.on('data', function(inputStdin) {
    inputString += inputStdin;
});

process.stdin.on('end', function() {
    inputString = inputString.split('\n');

    main();
});

function readLine() {
    return inputString[currentLine++];
}

/*
 * Complete the 'migratoryBirds' function below.
 *
 * The function is expected to return an INTEGER.
 * The function accepts INTEGER_ARRAY arr as parameter.
 */

// actual code 
function migratoryBirds(arr) {
    // Write your code here
    let obj={}
    // adding element with its number of occurence
  for(let i=0;i<arr.length;i++){
    if(obj[arr[i]]==undefined){
      obj[arr[i]]=1
    }else{
      obj[arr[i]]++
    }
  }
  let max=-Infinity
  let ans=""
  // checking element with max frequency and also max val
  for(let key in obj){
    if(max<obj[key]){
      max=obj[key]
      ans=key
    }
  }
  return ans
}

function main() {
    const ws = fs.createWriteStream(process.env.OUTPUT_PATH);

    const arrCount = parseInt(readLine().trim(), 10);

    const arr = readLine().replace(/\s+$/g, '').split(' ').map(arrTemp => parseInt(arrTemp, 10));

    const result = migratoryBirds(arr);

    ws.write(result + '\n');

    ws.end();
}