How to Convert a Date to Timestamp in JavaScript

Introduction

In programming, we often need to deal with dates and times, which can be represented in a few different ways, like an object (via Date), a string (i.e. "2023-10-04T00:00:00.000Z"), or a timestamp (i.e. 1696377600000). In this Byte, we'll explore how to convert a date or date string to a timestamp in JavaScript.

Why Convert Date or Date String to Timestamp

But why do we need to convert a date or date string to a timestamp in the first place? Timestamps are a more universal way of storing date and time information. They represent the number of seconds (or milliseconds) since the Unix Epoch (January 1, 1970), making them a simple way to store date and time data. They're also timezone-agnostic, which can simplify things when dealing with data from different time zones.

Dates and Timestamps in JavaScript

Before we get into converting our dates, let's take a moment to understand what we're dealing with. In JavaScript, a Date object represents a moment in time. You can create a new Date object with the new Date() constructor.

On the other hand, a timestamp is a numeric representation of a date, as described earlier.

let currentDate = new Date();
console.log(currentDate); // Outputs: 2023-10-04T13:20:23.670Z

How to Convert a Date to Timestamp

Converting a Date object to a timestamp in JavaScript is pretty straightforward. You can use the getTime() method, which returns the number of milliseconds since the Unix Epoch.

let currentDate = new Date();
let timestamp = currentDate.getTime();
console.log(timestamp); // Outputs: 1696425660603

Note: The getTime() method returns the timestamp in milliseconds. If you need the timestamp in seconds, you can divide the result by 1000.

How to Convert a Date String to Timestamp

So what if we have a date in string format? It'll be a similar process as before, but with the extra step of converting the string to a Date object and then the timestamp.

Just make sure your date string is in a format that the Date constructor can understand. According to MDN:

The JavaScript specification only specifies one format to be universally supported: the date time string format, a simplification of the ISO 8601 calendar date extended format. The format is as follows:
 
YYYY-MM-DDTHH:mm:ss.sssZ

Apparently other formats do work, but are implementation-dependent and may not work across all browsers.

let dateString = "2023-10-04";
let dateObject = new Date(dateString);
let timestamp = dateObject.getTime();
console.log(timestamp); // Outputs: 1696377600000

So the date string should be in a format recognized by the Date.parse() method (used internally by the Date constructor). While the above format is formally specified, you can also use more shorthand dates like "YYYY-MM-DD".

Other Solutions

While we've focused on the Date object and its getTime() method for converting a date to a timestamp in JavaScript, there are other ways to achieve the same thing. For instance, the valueOf() method returns the primitive value of a Date object as a number data type, which is the timestamp.

Here's an example:

let date = new Date();
console.log(date.valueOf()); // Output: 1696428432208

The + operator can also be used to convert a Date object to a timestamp. This works because the + operator triggers the valueOf() method behind the scenes in order to do any mathematical operation on the date.

let date = new Date();
console.log(+date); // Output: 1696428432208

Note: While these methods achieve the same result, it's important to understand how they work and when to use them. The + operator, for example, might be less clear to someone reading your code than the explicit getTime() or valueOf() methods.

Common Errors and How to Avoid Them

A common mistake when working with dates and timestamps in JavaScript is not accounting for time zones. JavaScript's Date object is based on the user's local time zone, but timestamps are always UTC. This can lead to unexpected results if not handled correctly.

For example, let's say you create a Date object for midnight on a specific date:

let date = new Date('2023-10-04T00:00:00');
console.log(date.getTime()); // Output: 1696428432208

Depending on your local time zone, the timestamp might not represent midnight UTC, but some other time. To avoid this, always create Date objects in UTC when you plan to convert them to timestamps.

Another common mistake is using the Date.parse() method to convert a date string to a timestamp. While this can work, it's not recommended because Date.parse() has inconsistent behavior across different browsers and can lead to some very hard-to-find bugs!

Use-Cases of Date/Timestamp Conversion

Converting dates to timestamps is useful in many situations. For example, timestamps are often used in APIs and databases to record when an event occurred. By storing the time as a timestamp, you can easily compare times and calculate durations—something that's much harder, or more error-prone, with date strings.

Timestamps are also handy for performance testing. By taking a timestamp at the start and end of a process, you can calculate how long it took. This is a common technique in JavaScript and other programming languages. You'd do this by creating new Date objects at the start/end of the process, but then you'd need to convert to timestamp to be able to find the difference between the two.

Conclusion

In this Byte, we've learned how to convert a date to a timestamp in JavaScript using the Date object's getTime() method. We've also looked at alternative methods, common errors to avoid, and some use-cases for date and timestamp conversion.