Reduce array of object to totals by property object
You need to return totals after you modify it:
const src = [{mon:1,tue:0,wed:3,thu:5,fri:7,sat:0,sun:4}, {mon:5,tue:3,wed:2,thu:0,fri:1,sat:0,sun:6}];
const res = src.reduce((totals, item) => {
Object.keys(item).forEach(weekday => totals[weekday] = (totals[weekday] || 0) + item[weekday]);
return totals;
}, {});
console.log(res);You need to return totals as accumulator for reduce.
If you have allways all days in the objects and you don't mind to mutate the first object, you could work without a start object.
const
src = [{ mon: 1, tue: 0, wed: 3, thu: 5, fri: 7, sat: 0, sun: 4 }, { mon: 5, tue: 3, wed: 2, thu: 0, fri: 1, sat: 0, sun: 6 }],
res = src.reduce((totals, item) =>
(Object.keys(item).forEach(d => totals[d] += item[d]), totals));
console.log(res);