JavaScript Math Object and Date/Time

JavaScript provides two powerful built-in objects for working with numbers and dates: the Math object and the Date object. These built-in tools save developers from writing complex mathematical logic or date handling code from scratch.

The Math Object

The Math object is a built-in JavaScript object that contains mathematical constants and functions. It does not need to be created — it is always available.

Math Constants

console.log(Math.PI);     // 3.141592653589793
console.log(Math.E);      // 2.718281828459045
console.log(Math.SQRT2);  // 1.4142135623730951

Rounding Methods

Math.round() — Round to Nearest Integer

console.log(Math.round(4.5));   // 5
console.log(Math.round(4.4));   // 4
console.log(Math.round(-3.6));  // -4

Math.floor() — Round Down (Towards Negative Infinity)

console.log(Math.floor(4.9));   // 4
console.log(Math.floor(4.1));   // 4
console.log(Math.floor(-3.1));  // -4

Math.ceil() — Round Up (Towards Positive Infinity)

console.log(Math.ceil(4.1));    // 5
console.log(Math.ceil(4.9));    // 5
console.log(Math.ceil(-3.9));   // -3

Math.trunc() — Remove Decimal, No Rounding

console.log(Math.trunc(4.9));   // 4
console.log(Math.trunc(-4.9));  // -4

Math.abs() — Absolute Value (Remove Negative Sign)

console.log(Math.abs(-15));  // 15
console.log(Math.abs(15));   // 15

Math.max() and Math.min() — Find Largest and Smallest

console.log(Math.max(10, 50, 30, 90, 20));  // 90
console.log(Math.min(10, 50, 30, 90, 20));  // 10

// With an array, use spread operator
let scores = [75, 88, 62, 91, 70];
console.log(Math.max(...scores));  // 91
console.log(Math.min(...scores));  // 62

Math.pow() — Power (Exponentiation)

console.log(Math.pow(2, 10));  // 1024
console.log(Math.pow(5, 3));   // 125

Math.sqrt() — Square Root

console.log(Math.sqrt(16));   // 4
console.log(Math.sqrt(144));  // 12

Math.random() — Random Number Between 0 and 1

Math.random() returns a decimal number between 0 (inclusive) and 1 (exclusive).

console.log(Math.random());  // e.g., 0.7342891...

// Random whole number between 1 and 10
let random = Math.floor(Math.random() * 10) + 1;
console.log(random);  // e.g., 7

// Random number between min and max (inclusive)
function getRandomInt(min, max) {
  return Math.floor(Math.random() * (max - min + 1)) + min;
}

console.log(getRandomInt(5, 15));  // e.g., 11

Math.log() — Logarithm

console.log(Math.log(Math.E));  // 1 (natural log)
console.log(Math.log2(8));      // 3 (log base 2)
console.log(Math.log10(1000));  // 3 (log base 10)

The Date Object

The Date object in JavaScript provides methods to work with dates and times. It can read the current date and time, create specific dates, compare dates, and format them.

Creating a Date Object

// Current date and time
let now = new Date();
console.log(now);
// e.g., Sun Mar 08 2026 14:30:00 GMT+0530

// Specific date
let birthday = new Date("1995-06-15");
console.log(birthday);

// Date with time
let meeting = new Date("2026-03-10T09:30:00");
console.log(meeting);

Getting Date Components

let today = new Date();

console.log(today.getFullYear());   // e.g., 2026
console.log(today.getMonth());      // 0-11 (0 = January)
console.log(today.getDate());       // 1-31 (day of month)
console.log(today.getDay());        // 0-6 (0 = Sunday)
console.log(today.getHours());      // 0-23
console.log(today.getMinutes());    // 0-59
console.log(today.getSeconds());    // 0-59
console.log(today.getTime());       // Milliseconds since Jan 1, 1970

Important: getMonth() returns 0 for January, 1 for February, and so on. Always add 1 for display purposes.

let today = new Date();
let displayMonth = today.getMonth() + 1;
console.log("Current month:", displayMonth);  // e.g., 3 (for March)

Setting Date Components

let date = new Date();
date.setFullYear(2027);
date.setMonth(11);   // December (0-indexed)
date.setDate(25);    // 25th day

console.log(date);   // Dec 25, 2027

Formatting Dates for Display

let today = new Date();

// Using toLocaleDateString()
console.log(today.toLocaleDateString());
// e.g., "3/8/2026" (varies by locale)

// Formatted with options
let options = { year: "numeric", month: "long", day: "numeric" };
console.log(today.toLocaleDateString("en-IN", options));
// e.g., "8 March 2026"

// ISO Format
console.log(today.toISOString());
// e.g., "2026-03-08T09:00:00.000Z"

Calculating Time Difference

Dates can be subtracted in JavaScript. The result is in milliseconds.

let startDate = new Date("2025-01-01");
let endDate   = new Date("2026-01-01");

let diffMs   = endDate - startDate;                   // Milliseconds
let diffDays = Math.floor(diffMs / (1000 * 60 * 60 * 24));  // Convert to days

console.log(diffDays + " days between dates.");  // 365 days between dates.

Countdown Timer Example

let today = new Date();
let newYear = new Date("2027-01-01");

let msLeft = newYear - today;
let daysLeft = Math.floor(msLeft / (1000 * 60 * 60 * 24));

console.log(`Days until New Year 2027: ${daysLeft}`);

Practical Example — Age Calculator

function calculateAge(birthDateStr) {
  let birthDate = new Date(birthDateStr);
  let today = new Date();

  let age = today.getFullYear() - birthDate.getFullYear();
  let monthDiff = today.getMonth() - birthDate.getMonth();

  if (monthDiff < 0 || (monthDiff === 0 && today.getDate() < birthDate.getDate())) {
    age--;  // Birthday hasn't happened yet this year
  }

  return age;
}

console.log(calculateAge("1995-06-15"));  // e.g., 30

Key Points to Remember

• The Math object provides mathematical constants and functions — no need to create it
• Math.round() rounds to nearest, Math.floor() rounds down, Math.ceil() rounds up
• Math.random() returns a decimal between 0 and 1 — use with Math.floor() to get integers
• Math.max() and Math.min() work with the spread operator ... on arrays
• Use new Date() to get the current date and time
• getMonth() returns 0–11 (January = 0) — always add 1 for display
• Subtracting two Date objects gives the difference in milliseconds
• Use toLocaleDateString() to format dates for display