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This article will explain in detail what the focus refers to. The editor thinks it is very practical, so I share it for you as a reference. I hope you can get something after reading this article.

Focus has three meanings, namely: 1, in JavaScript, the focus is the area of attention, that is, the current location of the cursor is activated; 2, in geometric mathematics, focus refers to the special point of the construction curve; 3, in physics, focus refers to an optical system has two focal points, namely the object focus and the image focus.

What does focus mean?

In fact, focus has three meanings:

1. In JavaScript, the focus is the area of attention, that is, where the current cursor is activated, and a small vertical bar that flashes on the page screen, indicating that a control on the page is selected and can be manipulated. Click the mouse to get the cursor, and the Tab key can switch focus according to the set Tabindex.

Methods for JavaScript to get focus and move focus away:

JavaScript can get the focus through the focus () method and move the focus away by the blur () method.

two。 In geometric mathematics, focus (focus or foci) (UK: / fo "ka" /, USA: / fo "sa" /), focus refers to the special points at which curves are constructed. For example, one or two focal points can be used to define a conical section, the four types of which are circular, elliptical, parabolic and hyperbolic. In addition, two focal points are used to define Cassini ellipses and Cartesian ellipses, and more than two focal points are used to define n-ellipses.

3. In physics, focus means that an optical system has two focal points: the object focus and the image focus. The object focus is the position of the object at infinity, and the image focus is the image position of the object at infinity. There are two ways to determine the position of the two focal points. One is the front focal length and the rear focal length relative to the first side and the last side of the system. The front focal length is the distance between the object focus and the first side of the system, and the rear focal length is the distance between the image focus and the last side of the system. Another method is relative to the principal plane of the system, that is, the so-called principal focal length, the object main focal length or the first principal focal length, which is the distance of the object focus from the first principal plane of the system, such as the square principal focal length or the second principal focal length. is the distance of the image focus from the second principal plane of the system. The focal length value of a system often refers to the main focal length value. The plane perpendicular to the common axis of the optical system and passing through the focal plane is the focal plane. Because there are two focal planes, there are also two focal planes: the first focal plane (object square focal plane) and the second focal plane (like square focal plane).

This is the end of the article on "what does focus mean?". I hope the above content can be of some help to you, so that you can learn more knowledge. if you think the article is good, please share it for more people to see.

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