Скачать или смотреть Why You Can't Override Math.PI But Can Override Math.floor in JavaScript

Discover the reasons behind JavaScript's behavior with `Math.PI` and `Math.floor`. Learn how property descriptors affect overriding and what it means for your code.
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Understanding JavaScript's Math Properties: Why Math.PI Cannot Be Overridden

JavaScript provides a built-in Math object that offers an abundance of helpful mathematical constants and functions. However, you may run into situations where you're curious about why certain methods can be overridden while others cannot. One common question arises around the properties of Math: Why can't I override Math.PI, but I can override Math.floor?

In this post, we will dive into this question, exploring why some properties are immutable and how you can check their characteristics using JavaScript.

The Problem: Attempting to Override Immutable Properties

When you attempt to perform an operation like:

[[See Video to Reveal this Text or Code Snippet]]

you might expect the value of Math.PI to change. Alas, upon logging the value of Math.PI, you will find that it remains as 3.141592653589793. This contrasts sharply with when you try to override a function such as Math.floor:

[[See Video to Reveal this Text or Code Snippet]]

Here, if you call Math.floor(), you'll see your overridden function taking effect. So, what is happening behind the scenes with these two properties?

Exploring Property Descriptors

JavaScript objects have descriptors that define the behavior of their properties. To understand the characteristics of Math.PI, we can leverage the Object.getOwnPropertyDescriptor() method. This method returns an object that describes the configuration of a property, including whether it is writable, enumerable, and configurable.

Check the Descriptor of Math.PI

You can check the property descriptor of Math.PI by running this code:

[[See Video to Reveal this Text or Code Snippet]]

The output will look something like this:

[[See Video to Reveal this Text or Code Snippet]]

Breaking Down the Descriptor

value: This is the constant value of Math.PI.

writable: This is set to false, which means you cannot change the value of Math.PI.

enumerable: This is set to false, indicating that the property does not show up in a loop that iterates over the object's properties.

configurable: This is also set to false, meaning you cannot delete the property or change its attributes.

Why Math.floor Can Be Overridden

In contrast, when you check the property descriptor for Math.floor, you’ll find that it has different attributes:

[[See Video to Reveal this Text or Code Snippet]]

This might yield something like:

[[See Video to Reveal this Text or Code Snippet]]

The writable attribute is true, which allows you to redefine the Math.floor function. The configurable attribute is also true, which not only allows you to change the function but also to delete it from the Math object entirely.

Conclusion

The stark differences between Math.PI and Math.floor boil down to their property descriptors. While Math.PI is designed to be a constant and immutable value to ensure consistency and reliability, Math.floor serves as a utility function meant to be flexible and customizable.

If you're ever in doubt about whether a property can be changed in JavaScript, always check its descriptor using Object.getOwnPropertyDescriptor(). This small step will arm you with knowledge about the nature of the properties you're working with, making your programming experience smoother and more predictable.

Maintaining an understanding of these nuances can enhance your JavaScript prowess, allowing you to write more effective and reliable code.