Why write script type text javascript when the mime type is set by the server

Question

My understanding is that mime types are set by the web server  Why do we add the type  text javascript or type  text css  attribute  Isn t this a useless and ignored attribute

User · Answer

It allows browsers to determine if they can handle the scripting/style language before making a request for the script or stylesheet (or, in the case of embedded script/style, identify which language is being used).

This would be much more important if there had been more competition among languages in browser space, but VBScript never made it beyond IE and PerlScript never made it beyond an IE specific plugin while JSSS was pretty rubbish to begin with.

The draft of HTML5 makes the attribute optional.

User · Answer

Douglas Crockford says      type  text javascript       This attribute is optional  Since   Netscape 2  the default programming   language in all browsers has been   JavaScript  In XHTML  this attribute   is required and unnecessary  In HTML    it is better to leave it out  The   browser knows what to do    He also says      W3C did not adopt the language   attribute  favoring instead a type   attribute which takes a MIME type    Unfortunately  the MIME type was not   standardized  so it is sometimes    text javascript  or    application ecmascript  or something   else  Fortunately  all browsers will   always choose JavaScript as the   default programming language  so it is   always best to simply write  lt script gt     It is smallest  and it works on the   most browsers    For entertainment purposes only  I tried out the following five scripts     lt script type  application ecmascript  gt alert  1    lt  script gt     lt script type  text javascript  gt alert  2    lt  script gt     lt script type  baloney  gt alert  3    lt  script gt     lt script type    gt alert  4    lt  script gt     lt script  gt alert  5    lt  script gt    On Chrome  all but script 3  type  baloney   worked   IE8 did not run script 1  type  application ecmascript   or script 3   Based on my non-extensive sample of two browsers  it looks like you can safely ignore the type attribute  but that it you use it you better use a legal  browser dependent  value

User · Answer

Boris Zbarsky  Mozilla   who probably knows more about the innards of Gecko than anyone else  provided at http   lists w3 org Archives Public public-html 2009Apr 0195 html the pseudocode repeated below to describe what Gecko based browsers do   if   type not set or empty       if   language not set or empty            Treat as default script language  what this is depends on the         content-script-type HTTP header or equivalent META tag      else        if   language is one of  javascript    livescript    mocha                                 javascript1 0    javascript1 1                                 javascript1 2    javascript1 3                                 javascript1 4    javascript1 5                                 javascript1 6    javascript1 7                                 javascript1 8               Treat as javascript        else             Treat as unknown script language  do not execute               else      if   type is one of  text javascript    text ecmascript                           application javascript                           application ecmascript                           application x-javascript             Treat as javascript      else           Treat as specified  e g  if pyxpcom is installed and         python script is allowed in this context and the type         is one that the python runtime claims to handle  use that           If we don t have a runtime for this type  do not execute

User · Answer

Because  at least in HTML 4 01 and XHTML 1  1   the type attribute for  lt script gt  elements is required   In HTML 5  type is no longer required   In fact  while you should use text javascript in your HTML source  many servers will send the file with Content-type  application javascript  Read more about these MIME types in RFC 4329   Notice the difference between RFC 4329  that marked text javascript as obsolete and recommending the use of application javascript  and the reality in which some browsers freak out on  lt script gt  elements containing type  application javascript   in HTML source  not the HTTP Content-type header of the file that gets send   Recently  there was a discussion on the WHATWG mailing list about this discrepancy  HTML 5 s type defaults to text javascript   read these messages with subject Will you consider about RFC 4329

[javascript] Why write <script type="text/javascript"> when the mime type is set by the server?

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