Issue pushing to array from nested loop

Question

When i run this everything works correctly except for the array pushing. The console.log(notificationdata); shows that notification data get it's values updated correctly but then looking at console.log(notifications) I have 7 identical ones with values matching the last one from notificationdata. Somehow pushing to the array is not happening correctly and I seem unable to figure it out. Any ideas?

var notifications = [];
reminder.days.value = ["Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday", "Sunday"]
reminder.times = [00:00]

      var notificationdata = {
        title: "Nu är det dags att ta en dos",
        text: "Ta " + medication + " mot " + affliction + " nu.",
        smallIcon: "../images/DosAvi_badge.png",
        icon: "../images/DosAvi_icon.png",
        every: "week",
        foreground: true
      }
      notificationdata.id = reminder.id;
      for(const day of reminder.days.value){
        for(const time of reminder.times){
          notificationdata.firstAt = getNextDayOfTheWeek(day, new Date(`Mon Jan 01 2020 ${time}`));
          //notificationdata.firstAt = new Date(`Wen Feb 26 2020 21:55`);
          console.log(notificationdata);
          notifications.push(notificationdata);
        }
      }
      console.log(notifications)

      cordova.plugins.notification.local.schedule(notifications);
    }

You can try not using const in for of so the time and day might change. Change it to let or just var. — Mortimer
– Mortimer, Commented Feb 26, 2020 at 23:47

Auskennfuchs · Accepted Answer · 2020-02-26 23:46:54Z

1

notificationdata is an object and inside your loop you're just changing a property of this object. The push to the array adds a reference of the object to the array. So you end up with an array of 7 references to the same object. To fix this you've to copy the object first:

      for(const day of reminder.days.value){
        for(const time of reminder.times){
          const copyNotificationdata = {
              ...notificationdata,
              firstAt: getNextDayOfTheWeek(day, new Date(`Mon Jan 01 2020 ${time}`))
          }
          notifications.push(copyNotificationdata);
        }
      }

answered Feb 26, 2020 at 23:46

Auskennfuchs

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Comments

Vočko · Accepted Answer · 2020-02-26 23:52:44Z

0

Because you don't create a new object and just reuse the same.

Javascript object variable only holds a reference to an object. It means that you always update the same data in the memory and your array holds 7 references to the same object.

You have to create a new object and insert it into your array:

for(const day of reminder.days.value){
    for(const time of reminder.times){
        const newNotificationdata = { ...notificationData };
        newNotificationdata.firstAt = getNextDayOfTheWeek(day, new Date(`Mon Jan 01 2020 ${time}`));
        notifications.push(newNotificationdata);
    }
}

edited Feb 26, 2020 at 23:52

answered Feb 26, 2020 at 23:46

Vočko

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