What is the purpose of using // in the following code. If old browsers doesnt support javascript then the symbols <!-- --> will ignore js code. In case browsers support JS, these symbols <!-- --> will be ignored. Then wats the use of // symbols.
<html>
<body>
<script type="text/javascript">
<!--
document.getElementById("demo").innerHTML=Date();
//-->
</script>
</body>
</html>
What is the purpose of using // in the following code. If old browsers doesnt support javascript then the symbols <!-- --> will ignore js code. In case browsers support JS, these symbols <!-- --> will be ignored. Then wats the use of // symbols.
<html>
<body>
<script type="text/javascript">
<!--
document.getElementById("demo").innerHTML=Date();
//-->
</script>
</body>
</html>
5 Answers
Reset to default 7If old browsers doesnt support javascript then the symbols
<!-- -->will ignore js code.
True, assuming HTML and for a definition of "old browsers" equal to "Netscape 1 era". Don't use them today.
In case browsers support JS, these symbols
<!-- -->will be ignored.
Only half true. Only the start of the ment is special cased. From the specification:
The JavaScript engine allows the string "
<!--" to occur at the start of a SCRIPT element, and ignores further characters until the end of the line. JavaScript interprets "//" as starting a ment extending to the end of the current line. This is needed to hide the string "-->" from the JavaScript parser.
-- is a JavaScript operator. It is used not to confuse the parser.
You really don't need those HTML ments anymore, BTW.
This is a non-standard feature that browsers and JavaScript engines have always implemented. Nowadays, it cannot be removed, as that would break backwards patibility. It’s detailed in the JavaScript / Web ECMAScript spec:
<!--must be treated as the start of aSingleLineComment— equivalent to//.var x = true; <!-- x = false; // note: no syntax error x; // true
-->at the start of a line, optionally preceded by whitespace orMultiLineComments, must be treated as aSingleLineComment— equivalent to//.var x = true; --> x = false; // note: no syntax error x; // true var x = 1; /* multiline ment! x = 2; */ --> x = 3; x; // 1
See HTML Comments and JavaScript
they are also use so that old versions of netscape dont through errors: http://www.yourhtmlsource./javascript/basicjavascript.html