Array of Dates

[シモダフランジポータルサイト]

I'm afraid this beginner question will bore the reader, but allow me to ask about the next function, which outputs the array filled with the same dates.

Where is incorrect?

function Test_DateArray(){

  let MyDate = new Date();

  let MyDates = [];

  for(let i= 1; i < 5; i++){

    MyDate.setDate(MyDate.getDate() + 1);

    MyDates.push(MyDate);

    Logger.log(MyDates);

  }

}

[DME]

Good beginner question 👍 — this one actually teaches a very important JavaScript concept.

❌ What’s going wrong?

You are pushing the SAME Date object reference into the array again and again.

👉 Date is an object, not a value type.
So when you do this:

MyDates.push(MyDate);

you’re not saving a new date — you’re saving a reference to the same object.
Later, when MyDate changes, all array entries point to that updated date, so they look identical.

Think of it like this 🧠
📌 You’re putting the same diary into the cupboard 4 times — not 4 different diaries.

---

🔍 Your code flow (simplified)

1. Create one Date object → MyDate

2. Modify it in each loop (setDate)

3. Push same object into array each time

4. Result → array shows same final date everywhere ❌

---

✅ Correct way: push a COPY of the Date

You must create a new Date instance for each entry.

✔️ Fix #1 (Recommended)

function Test_DateArray(){
  let MyDate = new Date();
  let MyDates = [];

  for (let i = 1; i < 5; i++) {
    MyDate.setDate(MyDate.getDate() + 1);
    MyDates.push(new Date(MyDate)); // ✅ clone date
  }

  Logger.log(MyDates);
}

---

✔️ Fix #2 (Cleaner approach)

Avoid mutating the same date at all:

function Test_DateArray(){
  let MyDates = [];

  for (let i = 1; i < 5; i++) {
    let d = new Date();
    d.setDate(d.getDate() + i);
    MyDates.push(d);
  }

  Logger.log(MyDates);
}

---

🧠 Key Concept (Very Important)

Type	Behavior
Number / String	Copied by value
Object / Array / Date	Copied by reference

So always remember:

Push objects by cloning, not reusing 🔁

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Deepak Bansode DME +91-7038193209 produ...@jalaramfeeds.com www.jalaramfeeds.com