Why Does JavaScript\'s `Date` Constructor Use a Zero-Based Month?

JavaScript Date Constructor: Unveiling the Zero-Based Month Argument

When creating a JavaScript Date object, you may have noticed that the month argument starts from 0 instead of 1. This peculiarity can lead to confusion, especially since the day of the month argument is based on 1. Why is this discrepancy present, and is there a logical reason behind it?

The answer lies in the historical evolution of JavaScript's Date constructor. As Brendan Eich, the creator of JavaScript, explained on Twitter, JavaScript's Date was inspired by Java's java.util.Date, which also used a zero-based month system.

Originally, JavaScript aimed to emulate Java's API to facilitate cross-language compatibility. Unfortunately, this meant inheriting quirks like the zero-based month argument. Ken Smith of Netscape helped port the Java code to C for JavaScript's implementation.

Despite the initial design choice, developers have long recognized the inconvenience of this zero-based system. The java.util.Calendar class introduced in Java 1.1 provided a better date/time API, but it still maintained the zero-based month convention.

JavaScript has lacked a robust, built-in date/time API, leaving developers to rely on third-party libraries like Luxon, Moment.js, and date-fns. These libraries address the limitations of the Date object and provide more intuitive date handling.

The TC39 Temporal proposal aims to address this deficiency by introducing a modern date/time API into JavaScript. This proposal, if implemented, would bring JavaScript's date handling up to date with current best practices, providing a more consistent and user-friendly approach.

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