JSFiddle - React, Tailwind, and code Playground

JavaScript

var data = {"students": [{"student": "John", "status": "pass", "subject": "english"},{"student": "Joe", "status": "pass", "subject": "english"},{"student": "Jill", "status": "fail", "subject": "french"}]};

var res = {};

for (var i in data.students)
{
    var item = data.students[i];
    var subject = item.subject;

    if (!res[subject])
        res[subject] = { passedCount: 0, failedCount: 0 };

    if (item.status == 'pass')
        res[subject].passedCount++;
    else
        res[subject].failedCount++;
}

document.body.innerHTML = JSON.stringify(res);