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addSeconds.md

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title addSeconds()

Adds or subtracts seconds from a Date object.

Syntax

addSeconds(dateObj, seconds)

Parameters

Parameter Type Required Description
dateObj Date Yes The base Date object
seconds number Yes Number of seconds to add (positive) or subtract (negative)

Returns

Date - A new Date object with the specified number of seconds added or subtracted

Basic Examples

Adding and Subtracting Seconds

import { addSeconds } from 'date-and-time';

const date = new Date(2024, 7, 15, 14, 30, 45, 123);  // August 15, 2024 14:30:45.123

// Add seconds
const future = addSeconds(date, 30);
console.log(future);  // August 15, 2024 14:31:15.123

// Subtract seconds
const past = addSeconds(date, -20);
console.log(past);  // August 15, 2024 14:30:25.123

Use Cases

Countdown Timers

function createCountdown(duration: number): { start: Date, end: Date, remaining: () => number } {
  const start = new Date();
  const end = addSeconds(start, duration);
  
  return {
    start,
    end,
    remaining: () => Math.max(0, Math.floor((end.getTime() - Date.now()) / 1000))
  };
}

const countdown = createCountdown(300); // 5 minute countdown
console.log(`Countdown ends at: ${countdown.end.toLocaleTimeString()}`);
console.log(`Time remaining: ${countdown.remaining()} seconds`);

// Use in a timer
const updateCountdown = () => {
  const remaining = countdown.remaining();
  if (remaining > 0) {
    console.log(`${remaining} seconds left`);
    setTimeout(updateCountdown, 1000);
  } else {
    console.log('Time up!');
  }
};

updateCountdown();

Precise Time Intervals

function generateTimeIntervals(startTime: Date, intervalSeconds: number, count: number): Date[] {
  const intervals: Date[] = [];
  let currentTime = new Date(startTime);  

  for (let i = 0; i < count; i++) {
    intervals.push(new Date(currentTime));
    currentTime = addSeconds(currentTime, intervalSeconds);
  }
  
  return intervals;
}

const start = new Date(2024, 7, 15, 12, 0, 0);  // August 15, 2024 12:00:00
const intervals = generateTimeIntervals(start, 15, 8);  // Every 15 seconds, 8 times

console.log(intervals);
// [12:00:00, 12:00:15, 12:00:30, 12:00:45, 12:01:00, 12:01:15, 12:01:30, 12:01:45]

Immutability

addSeconds() does not modify the original Date object:

const originalDate = new Date(2024, 7, 15, 14, 30, 45);
const modifiedDate = addSeconds(originalDate, 120);

console.log(originalDate);  // August 15, 2024 14:30:45 (unchanged)
console.log(modifiedDate);  // August 15, 2024 14:32:45 (new object);

See Also