Why Does JavaScript\'s `Date` Object Use Zero-Based Month Indexing?

The Historical Anomaly of JavaScript's Zero-Indexed Months

When constructing a new Date object in JavaScript using the constructor, a peculiar observation arises: the month argument starts from 0. This deviation from intuitive numbering has perplexed developers for quite some time.

Despite the month argument being zero-indexed, the day of the month argument begins from 1. This inconsistency has further fueled curiosity as to the rationale behind such a design choice.

To demystify this historical anomaly, we venture into the annals of programming history:

Lineage from Java's Date API

Brendan Eich, the creator of JavaScript, revealed on Twitter that he adopted the Date API from Java's JDK1.0 (1995). Ken Smith of Netscape ported the java.util.Date class to JavaScript, resulting in the inheritance of this peculiar month indexing scheme.

Deprecation in Java but Persistence in JavaScript

Java eventually deprecated this anomalous behavior in JDK 1.1, favoring zero-based indexing. However, JavaScript has remained unchanged.

Modern Solutions and Future Prospects

While JavaScript lacks a built-in date/time API with corrected month indexing, numerous third-party libraries such as Luxon Moment.js, date-fns, and js-joda have emerged as viable alternatives.

On the horizon is the TC39 Temporal proposal, which aims to introduce a comprehensive and modern date/time system to the language. If adopted, JavaScript will finally escape the shackles of its historical quirk and embrace a user-friendly and intuitive month numbering.

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