是什么 <!— //--> 在ASP中意味着什么？

Question

<script language="javascript">
    <!--    
             //some logic here 
    //-->
</script>

What does <!-- //--> mean? . I thought they were comment, however, the double slash before --> puzzles me.

Answer 1

That has nothing to do with ASP. That's a historical artifact from when Javascript was new and not supported in all browsers. <!-- is a legitimate component of the JS language itself, and is treated as a "do nothing" command. --> however, is NOT part of JS, so you have to escape it using a proper JS comment, hence //-->

All this is just to hide the JS code from stoneage/obsolete browsers which didn't understand the <script> tag. Remember that browsers ignore tags which they don't recognize. A non-JS browser would skip over <script> and start outputting the JS code as text. Hence the comment sequence. Even if the browser doesn't understand <script> and </script> it WILL understand an HTML comment, and skip over all of the code.

Eg if you loaded a modern JS-enabled page in Netscape 1.0 and had something like:

<script>
  alert('hello, world!');
</script>
<foo>
  Hello again
</foo>

Then you wouldn't get an alert, you'd actually see

alert('hello, world!');Hello again

in the browser window. But if you had

<script>
<!--
   alert('hello, world!');
//-->
</script>
<foo>
   Hello again
</foo>

then you'd only see

 Hello again