Increment value of List Object array in Object array [duplicate]

Question

I create an object name month, List year and object list. Then I add list year to object list as keys and add object month to list of object list.

var year = [2021, 2020];
var month = {"jan": 0, "feb": 0, "mar": 0};
var list={};
for (let i = 0; i < 2; i++) {
    list[year[i]] = [month];
}
list['2021'][0]['feb']+=1;
console.log(list);

Result: list={'2021': [{'jan':0, 'feb':0, 'Mar':0}], '2020': [{'jan':0, 'feb':0, 'Mar':0}]}

Results as I wanted, but problem occurred when I try to increment the value of each month by year. Example: list['2021'][0]['feb']+=1;

What I want: list={'2021': [{'jan':0, 'feb':1, 'Mar':0}], '2020': [{'jan':0, 'feb':0, 'Mar':0}]}

What I get: list={'2021': [{'jan':0, 'feb':1, 'Mar':0}], '2020': [{'jan':0, 'feb':1, 'Mar':0}]}

Right. You have one month array, and you've just stored two references to that array. If you do list[year[i]] = [{"jan": 0, "feb": 0, "mar": 0}]; instead of using month, it should work. — Tim Roberts
– Tim Roberts, Commented Jan 20, 2023 at 7:25
change list[year[i]] = [month];to list[year[i]] = [{...month}]; and it should work (this will basically clone the month into a new object, instead of having the same object in both — dave
– dave, Commented Jan 20, 2023 at 7:27

Mandeep · Accepted Answer · 2023-01-20 07:45:32Z

0

Try This

var year = [2021, 2020];
var month = {"jan": 0, "feb": 0, "mar": 0};
var list={};
for (let i = 0; i < 2; i++) {
    list[year[i]] = [Object.assign({}, month)];
}
list['2021'][0]['feb']+=1;
console.log(list);

answered Jan 20, 2023 at 7:45

Mandeep

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