JavaScript Date valueOf() Method

Beginner
5 min read
Updated: Nov 2026
3 examples
Date
Decorative image with the word VALUEOF

Definition

Date.prototype.valueOf() returns the milliseconds since January 1, 1970 UTC (the Unix epoch) for that Date. It is functionally the same as getTime().

Remember
date.valueOf()

→ number (ms since 1970-01-01 UTC)
→ same as date.getTime()
→ NaN if the Date is invalid

new Date(0).valueOf()     → 0
+date                     → same idea (coercion)
dateB - dateA             → elapsed ms

Syntax

Call date.valueOf. Start with this line.

JavaScript
date.valueOf()
CallWhat it does
date.valueOf()Primary signature.
date.valueOf(...)Call with the arguments your case needs.

Built into JavaScript. Call valueOf(...) on a Date instance — no import required.

Library declarations
JavaScript
date.valueOf()

Parameters

ParameterDescription
dateRequired. Date instance to read

Return Value

Return ValueDescription
*Epoch ms (number), or NaN if invalid

JavaScript Examples

Example 1 — Read the Epoch Milliseconds

Call valueOf() on a UTC-built Date (MDN-style example).

JavaScript
const date1 = new Date(Date.UTC(96, 1, 2, 3, 4, 5));

console.log(date1.valueOf());
// 823230245000

const date2 = new Date("02 Feb 1996 03:04:05 GMT");

console.log(date2.valueOf());
// 823230245000
Try It Yourself

How It Works

  1. Build the same instant two ways. Date.UTC parts and a GMT string both mean Feb 2, 1996 03:04:05 UTC.
  2. Call valueOf(). Each Date returns its internal timestamp as a number.
  3. Same result. Both print 823230245000 because they store the same instant.
  4. Unit. The value is milliseconds since the Unix epoch — not a formatted date string.

Example 2 — valueOf() Equals getTime()

Confirm both methods return the same number for the same Date.

JavaScript
const d = new Date(0); // epoch

console.log(d.valueOf());  // 0
console.log(d.getTime());  // 0
console.log(d.valueOf() === d.getTime()); // true
Try It Yourself

How It Works

  1. Start at the epoch. new Date(0) is midnight UTC on Jan 1, 1970.
  2. Read with valueOf(). Zero milliseconds after the epoch → 0.
  3. Read with getTime(). Same internal value → also 0.
  4. They match. MDN treats them as functionally equivalent for Date.

Example 3 — Subtract Two Dates for Elapsed ms

Subtraction coerces each Date to a number (via the value-of path).

JavaScript
const a = new Date(Date.UTC(2026, 0, 1));
const b = new Date(Date.UTC(2026, 0, 2));

console.log(b.valueOf() - a.valueOf()); // 86400000
console.log(b - a);                     // 86400000 (1 day in ms)
Try It Yourself

How It Works

  1. Two UTC midnights. Jan 1 and Jan 2, 2026 — one day apart.
  2. Subtract the numbers. b.valueOf() - a.valueOf() is 86_400_000 ms.
  3. Or subtract the Dates. b - a coerces both sides to numbers and gets the same result.
  4. Why it helps. Epoch ms make duration math simple — divide by 1000 for seconds if needed.
Compatibility

Browser & Runtime Support

Date.prototype.valueOf() has been in JavaScript since ES1. It is Baseline and works in every modern browser and Node.js — no polyfill needed.

✓ Baseline · ES1

Date.prototype.valueOf()

Supported everywhere Date exists: Chrome, Firefox, Safari, Edge, Internet Explorer, and all Node.js versions.

99% Universal API
Google Chrome Supported · Desktop & Mobile
Full support
Mozilla Firefox Supported · Desktop & Mobile
Full support
Apple Safari Supported · macOS & iOS
Full support
Microsoft Edge Supported · Chromium
Full support
Internet Explorer No native support · Use a polyfill
Polyfill
Opera Supported · Modern versions
Full support
Samsung Internet Supported · Android
Full support
Bun Supported · JavaScript runtime
Supported
Deno Supported · JavaScript runtime
Supported
Node.js Supported · Server runtime
Supported
Android WebView Supported · Modern WebView
Full support
Date.valueOf() Excellent

Bottom line: Safe to use in any environment. Focus on equivalence with getTime() and NaN for invalid Dates. See also the MDN valueOf() reference.

Frequently Asked Questions

A number: milliseconds since January 1, 1970 00:00:00 UTC for that Date. It returns NaN if the Date is invalid. It does not return a Date object.
Yes for Date. valueOf() is functionally equivalent to getTime() — both return the same epoch milliseconds. Prefer getTime() when you want a clear “timestamp” call; valueOf() is the generic Object hook used in numeric coercion.
When a Date is coerced to a number — for example Number(date), +date, date - otherDate, or comparisons like dateA > dateB. Date also has Symbol.toPrimitive, which still uses valueOf() internally for the number path.
Compare the numbers: dateA.valueOf() < dateB.valueOf(). Subtracting two Dates (dateB - dateA) also works because both sides coerce to numbers.
NaN — the same as getTime() on an invalid Date. Check with Number.isNaN(date.valueOf()).
Date.now() is the current timestamp without a Date instance. valueOf() (or getTime()) reads the timestamp of an existing Date you already have.

Next: String Methods

Explore JavaScript string helpers after finishing Date methods.

String methods →

About the author

Mari Selvan M P
Mari Selvan M P 🔗

Developer, cloud engineer, and technical writer

  • Experience 12 years building web and cloud systems
  • Focus Full Stack Development, AWS, and Developer Education

I write practical tutorials so students and working developers can learn by doing—from databases and APIs to deployment on AWS.

AWS Certified Developer – Associate (Credly)

12 people found this page helpful

JavaScript Date.UTC() Method JavaScript String Methods