setFullYear()

ES1+

Sets the full year for a specified date according to local time.

Syntax

date.setFullYear(year, month, day)

Parameters

year number

An integer specifying the year

month number optional

An integer between 0 and 11 representing the month

day number optional

An integer between 1 and 31 representing the day of the month

Return Value

number

The number of milliseconds between the date and UNIX epoch

Examples

JavaScript

const date = new Date('2024-01-15');
date.setFullYear(2025);
console.log(date.getFullYear());
date.setFullYear(2026, 5, 20);
console.log(date.toLocaleDateString('ko-KR'));

Output:

// 2025 2026. 6. 20.

📌 When to Use

Use setFullYear() when you need to modify the year of an existing Date object, such as for date navigation or year-based calculations.

⚠️ Common Mistakes

Forgetting that setFullYear() mutates the original Date object instead of returning a new one.

Not accounting for leap year when setting February 29th on non-leap years.

✅ Best Practices

Clone the date before modifying if you need to preserve the original: new Date(date.getTime()).

Use setFullYear(year, month, day) to set all date components at once for atomicity.

⚡ Performance Notes

setFullYear() is O(1). It is more efficient than creating a new Date object for simple year changes.

🌍 Real World Example

Year Navigation Component

Navigate between years in a date picker or calendar component.

function createYearNavigator(initialDate) {
  let currentDate = new Date(initialDate);

  return {
    current: () => new Date(currentDate),

    goToYear: (year) => {
      const newDate = new Date(currentDate);
      newDate.setFullYear(year);
      currentDate = newDate;
      return currentDate;
    },

    nextYear: () => {
      const newDate = new Date(currentDate);
      newDate.setFullYear(newDate.getFullYear() + 1);
      currentDate = newDate;
      return currentDate;
    },

    prevYear: () => {
      const newDate = new Date(currentDate);
      newDate.setFullYear(newDate.getFullYear() - 1);
      currentDate = newDate;
      return currentDate;
    }
  };
}

const navigator = createYearNavigator('2024-06-15');
console.log(navigator.nextYear().getFullYear()); // 2025
console.log(navigator.goToYear(2020).getFullYear()); // 2020

Related Methods

getFullYear()