Get the Date of the Next Monday using JavaScript

Get the Date of the Next Monday using JavaScript #

To get the date of the next Monday:

1. Get the day of the month of the next Monday.
2. Pass the result to the setDate() method.
3. The setDate method changes the day of the month for the given date.

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function getNextMonday(date = new Date()) {
  const dateCopy = new Date(date.getTime());

  const nextMonday = new Date(
    dateCopy.setDate(
      dateCopy.getDate() + ((7 - dateCopy.getDay() + 1) % 7 || 7),
    ),
  );

  return nextMonday;
}

// 👇️ Get Monday of Next Week
console.log(getNextMonday(new Date())); // 👉️ Mon Jan 24 2022

// 👇️ Get Next Monday for specific Date
console.log(getNextMonday(new Date('2022-01-25'))); // 👉️ Mon Jan 31 2022

We created a reusable function that takes a Date object as a parameter and returns the next Monday.

If no parameter is provided, the function returns the next Monday of the current date.

The setDate method allows us to change the day of the month of a specific Date instance.

The method takes an integer that represents the day of the month.

To get the next Monday, we:

1. Add 1 to the day of the week, e.g. Tuesday = 7 - 2 (Tuesday) + 1 = 6. Note that the getDay() method returns the day of the week where Sunday is 0, Monday is 1, Tuesday is 2, etc.

2. Use the modulo operator to get the remainder of dividing 6 % 7 = 6

3. If the remainder is equal to 0, then the current date is Monday and we have to default it to 7 to get the date of the next Monday.

4. The getDate() method returns the day of the month, e.g. 18 + 6 = 24, where 24 is the day of the month for the next Monday.

If the Date object stores a Monday:

1. Get the day of the month, e.g. 17.
2. Calculate 7 - day of the week (Monday = 1) + 1 = 7
3. Get the remainder - 7 % 7 = 0 || 7 = 7.
4. Get the day of the month for the next Monday - 17 + 7 = 24, where 24 is the day of the month for the next Monday.

We created the dateCopy variable in the function because the setDate method mutates the Date instance in place.

If you use the same Date object elsewhere in your code, this might lead to confusing bugs.