Media type / application
application/javascript
The former media type for JavaScript, kept working by every browser but obsoleted in favour of text/javascript.
Obsolete: Send text/javascript instead. This spelling still works but is no longer the registered type.
Browser behaviour
Executes in the page
Charset
charset required
Compression
Compress in transit
Send it like this
Content-Type: application/javascript; charset=utf-8Send `; charset=utf-8`. Without it the receiver falls back to its own default — for some text types that default is us-ascii, and any non-ASCII character then renders wrong.
Handling verdict
Rendered inline, this type executes script in the origin that served it. Never serve untrusted content under it from an origin that holds sessions — use a separate origin, or force a download with Content-Disposition: attachment.
Send `; charset=utf-8`. Without it the receiver falls back to its own default — for some text types that default is us-ascii, and any non-ASCII character then renders wrong.
The payload is text-like or otherwise repetitive, so gzip or Brotli removes real bytes. Enable it at the server or CDN.
Registered with IANA through a public review process, so the name is stable and every implementation can rely on it meaning the same thing.
Anatomy of the name
RFC 6838Top-level type
application
Application
Subtype
javascript
Registered in the standards tree.
Structured syntax
none
No suffix, so the payload format is defined entirely by the subtype itself.
Parameters
charset
Beyond the charset rule above, this type defines no parameters of its own.
Response headers
Content-Type: application/javascript; charset=utf-8
X-Content-Type-Options: nosniff
Content-Disposition: inline
Content-Security-Policy: sandbox; default-src 'none'
Vary: Accept-Encodingnosniff stops the browser second-guessing the type you declared, which is what makes the rest of this reliable. The sandbox directive is the belt-and-braces option when the content is not fully under your control.
Server configuration
extension mappingnginx
types {
application/javascript js;
}Apache
AddType application/javascript .js
AddCharset UTF-8 .jsCaddy
@type path *.js
header @type Content-Type "application/javascript; charset=utf-8"Extensions and other spellings
declaredFile extensions
File signature
No fixed signature — this format has no reliable magic number, so identify it by parsing rather than by the first few bytes.