How to Reliably Determine the Last Day of a Month Across All Browsers?

Determining the Last Day of a Month Cross-Browser

The ability to calculate the last day of a month is a common requirement in many programming scenarios. One method to achieve this in JavaScript is by setting the day value of a Date object to 0.

Mozilla Documentation Ambiguity

According to the Mozilla documentation, setting the day value to 0 in Date.setFullYear results in the last day of the previous month. However, it remains unclear whether this behavior is consistent across all browsers.

Alternative Method

To ensure cross-browser compatibility, it is recommended to use the following method to calculate the last day of a 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 takes advantage of the fact that setting the day value to 0 in the JavaScript Date constructor results in the last day of the previous month.

Conclusion

While setting the day value to 0 in Date.setFullYear may work in some browsers, it is not a reliable cross-browser method. To ensure compatibility and accuracy, it is best to use the alternative method provided above.

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