Сложить данные из объектов с одинаковым значением

var data = [{ id: 100, chance: 10 }, { id: 100, chance: 30 }, { id: 200, chance: 10 }, 
            { id: 300, chance: 5 }, { id: 200, chance: 30 }, { id: 100, chance: 15 }]; 
var result = {}; 
for (var element of data) 
{ 
  if (result[element.id] == undefined) 
    result[element.id] = 0; 
  result[element.id] += element.chance; 
}  
for (var id in result) 
  console.log("id: " + id + ", chance: " + result[id]);

let data = [{ 
        id: 100, 
        chance: 10 
    }, 
    { 
        id: 100, 
        chance: 30 
    }, 
    { 
        id: 200, 
        chance: 10 
    }, 
    { 
        id: 300, 
        chance: 5 
    }, 
    { 
        id: 200, 
        chance: 30 
    }, 
    { 
        id: 100, 
        chance: 15 
    } 
]; 
let result = data.reduce((prev, item) => { 
	if (item.id in prev) { 
		prev[item.id] += item.chance 
	} else { 
		prev[item.id] = item.chance; 
	} 
	return prev; 
}, {}) 
Object.keys(result).forEach(id => { 
	console.log(`id:${id}, chance:${result[id]}`); 
})