Counting elements in array of objects using Lodash

lodash.ts

// without lodash
let currentGradeId;
let looper = 0;
let tempArray = {};
let finalArray = [];

this.items.forEach((obj, index) => {
    currentGradeId = this.items[index].grade_id;

    if (tempArray[currentGradeId] === undefined) {
        tempArray[currentGradeId] = looper;
        finalArray[looper] = {grade: currentGradeId, count: 1}
    } else {
        finalArray[tempArray[currentGradeId]]['count'] += 1;
    }

});

// with lodash
_.map(_.countBy(this.items, 'grade_id'), (value, key) => {
    return {grade: key, count: value};
});