How to subtract days from a plain Date?

Understanding the basics

Automatic rollovers with setDate()

With setDate(), month and year rollover are handled automatically:

let date = new Date(2020, 0, 1); // beginning of 2020
date.setDate(date.getDate() - 365); // Let's go back to 2019!
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That was a quick spin around the sun!

Acknowledge time zones and DST

When dates get tricky, it's usually because of Time Zones and Daylight Saving Time (DST). You might need to adjust for these changes:

let date = new Date(); 
const initialOffset = date.getTimezoneOffset(); // "Houston, we have an offset!"
date.setDate(date.getDate() - 5);
const newOffset = date.getTimezoneOffset(); // Updated offset 
if (initialOffset !== newOffset) {
  // Brace yourselves, DST changes are coming!
}
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Millisecond manipulation for extra precision

You can also "rewind" time by subtracting milliseconds directly from the time value:

let myDate = new Date(); 
myDate.setTime(myDate.getTime() - (24*60*60*1000 * 5)); // Back to the future... 5 days back!
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Remember: Time runs at about 246060*1000 milliseconds per day. You're not in Kansas anymore!

Advanced Time-Travel Hacks

Crafting your own Time Machine (Reusable Function)

Meet the McFly function, aka addOrSubtractDays, for date manipulation:

function addOrSubtractDays(date, days, add = true) {
  const dayMs = 24*60*60*1000; // One day = 86,400,000 ms; Keep the Flux Capacitor ready!
  const newTime = date.getTime() + (days * dayMs * (add ? 1 : -1));
  return new Date(newTime); // We've hit 88 miles an hour!
}
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This lets you add or subtract days flexibly, ensuring you retain your temporal integrity!

Libraries to save your time (& sanity!)

Consider using a modern JavaScript library like DateJS, date-fns, or Moment.js:

var moment = require('moment');
let momentDate = moment(date);
momentDate.subtract(5, 'days'); // Meet the future head-on... 5 days ago!
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These libraries pamper you with comprehensive date methods and shield you from DST nightmares and timezone trolls.

Stay sharp with edge cases

Remember to handle edge cases:

• Crossing month and year boundaries? Watch for those leap years.
• Just don't wander farther than the Unix epoch (January 1, 1970) unless you've packed a light saber.
• Crossing DST boundaries? Check your Flux Capacitor--er, verify date correctness.

Surprise folks with friendly date displays

Make sure your audience can read past the Matrix:

let date = new Date();
date.setDate(date.getDate() - 5);
console.log(date.toLocaleString());
// Print "5 days ago, The Matrix was still here!"
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Bullet time! Control your output with toLocaleDateString() for customizable formats.