Count All Unique Items in an Array Using JavaScript Function

We are required to write a JavaScript function that counts all unique items in an array. The function should return an object representing the count of each unique element of the array.

Let’s say the following is our array −

const arr = ["hi", "hello", "hi"];

Example

Following is the code −

const arr = ["hi", "hello", "hi"];
const countUnique = arr => {
   const counts = {};
   for (var i = 0; i < arr.length; i++) {
      counts[arr[i]] = 1 + (counts[arr[i]] || 0);
   };
   return counts;
};
console.log(countUnique(arr));

Output

This will produce the following output on console −

{ hi: 2, hello: 1 }