array_reducer_example_04.js

const survey = [
    { name: "Zuri", votedFramework: 'react' },
    { name: "Sofia", votedFramework: 'angular' },
    { name: "Elon", votedFramework: 'react' },
    { name: "Joe", votedFramework: 'react' },
    { name: "Alex", votedFramework: 'angular' },
    { name: "Josh", votedFramework: 'vue' },
    { name: "Jade", votedFramework: 'react' },
    { name: "Ted", votedFramework: 'angular' },
    { name: "Leo", votedFramework: 'react' },
    { name: "Nala", votedFramework: 'react' },
    { name: "Jack", votedFramework: 'react' },
    { name: "Fiadh", votedFramework: 'vue' },
];

const reducerCallback = (prevItem, vote, i) => { 
    if (prevItem[vote.votedFramework] === undefined) {
        return { ...prevItem, [vote.votedFramework]: [vote.name] }
    }

    prevItem[vote.votedFramework].push(vote.name)
    return { ...prevItem }
}

console.log(survey.reduce(reducerCallback, {}))

/* {
  "react": ["Zuri", "Elon", "Joe", "Jade", "Leo", "Nala", "Jack"],
  "angular": ["Sofia", "Alex", "Ted"],
  "vue": ["Josh", "Fiadh"]
} */