Using javascript to determine the IE version number is simple, practical and backward compatible_javascript skills

Today I need to determine the IE version number in a project, and because jQuery 2.0 removes the judgment of the browser version number (it recommends feature detection), I saw a piece of code written by a foreigner:

This code is really clever! Both brief and backward compatible! The general approach is: regular search for USER_AGENT;
However, due to historical reasons, USER_AGENT has always been inaccurate and has been changed in a mess by major manufacturers.

For example:

These What kind of messy strings are they? . . Who knows what IE12 will become! ! !
So using feature detection or USER-AGENT detection is neither reliable nor backwards compatible!

Highly recommend the above code!
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When I first learned programming, I felt that I knew a lot and had a lot to write about;
But after really learning a lot of knowledge in depth, I painfully discovered that I knew too little! I want to write something, but it’s hard to do it.