let arr = [

    { quarter: 12, title: 'hello' },

    { quarter: 13, title: '====' },

    { quarter: 12, title: 'word' }

];

​

let list = {};

arr.forEach((item) => {

    let key = item.quarter;

    list[key] = list[key] || [];

    list[key].push(item);

})

console.log(list);