Is Setting Date.setFullYear(year, month, 0) a Reliable Way to Find the Last Day of a Month Across Browsers?

Finding the Last Day of a Month Accurately

It is known that setting the day value in Date.setFullYear to 0 retrieves the last day of the previous month. For example:

<code class="js">d = new Date();
d.setFullYear(2008, 11, 0); // Returns Sun Nov 30 2008</code>

This behavior is documented on Mozilla's website. However, it raises the question of whether this cross-browser feature is reliable or if alternative methods should be considered.

Cross-Browser Compatibility

Unfortunately, this feature is not cross-browser compatible. While it works in most major browsers, including Chrome, Firefox, and Safari, it does not behave consistently in Internet Explorer. In Internet Explorer, setting the day value to 0 may not always return the last day of the previous month.

Alternative Methods

To ensure accuracy across multiple browsers, alternative methods for finding the last day of a month are recommended. One reliable approach is to use the Date.getMonth() method, which returns the month number (0-based). You can then subtract one from this value to obtain the previous month's number and set the date to the last day of that month:

<code class="js">var month = 0; // January
var d = new Date(2008, month + 1, 0);
console.log(d.toString()); // Last day in January</code>

This method accurately retrieves the last day of a month, regardless of the browser being used.

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