Conditional compilation _javascript techniques for JScript

Microsoft's interpretation of conditional compilation is:
Some typical uses of conditional compilation include using new features in Jscript, embedding debugging support in scripts, and tracking code running.

First look at a piece of code simple to understand:


var s=0//@cc_on +1
Alert (s)


If you are using IE you can see that the browser pop-up tip s is the value of "1";

var s=0//@cc_on +1
In IE is equivalent to:

var s=0+1

Conditional compilation provides a way to run code in a comment.

In general, we rarely use conditional compilation when writing JavaScript code. However, conditional compilation because of its own characteristics, for our detection system, automatic recognition of browser programming is convenient.
There's a classic piece of code:
var Ismsie =/* @cc_on!@*/false;

You can also do this:
var ie=0//@cc_on +1

A bit more complicated:

var ieversion=/* @cc_on function () {switch (@_jscript_version) {case 1.0:return 3, Case 3.0:return 4, Case 5.0:return 5; CAs e 5.1:return 5; Case 5.5:return 5.5; Case 5.6:return 6; Case 5.7:return 7; }}()|| @*/0;