express.static(root, [options])
This is the only built-in middleware function in Express. It serves static files and is based on serve-static.
The root argument refers to the root directory from which the static assets are to be served. The file to serve will be determined by combining req.url with the provided root directory. When a file is not found, instead of sending a 404 response, this module will instead call next() to move on to the next middleware, allowing for stacking and fall-backs.
The following table describes the properties of the options object.
| Property | Description | Type | Default |
|---|---|---|---|
dotfiles | Determines how dotfiles (files or directories that begin with a dot “.”) are treated. See dotfiles below. | String | “ignore” |
etag | Enable or disable etag generation NOTE: express.static always sends weak ETags. | Boolean | true |
extensions | Sets file extension fallbacks: If a file is not found, search for files with the specified extensions and serve the first one found. Example: ['html', 'htm']. | Boolean | false |
fallthrough | Let client errors fall-through as unhandled requests, otherwise forward a client error. See fallthrough below. | Boolean | true |
index | Sends the specified directory index file. Set to false to disable directory indexing. | Mixed | “index.html” |
lastModified | Set the Last-Modified header to the last modified date of the file on the OS. | Boolean | true |
maxAge | Set the max-age property of the Cache-Control header in milliseconds or a string in ms format. | Number | 0 |
redirect | Redirect to trailing “/” when the pathname is a directory. | Boolean | true |
setHeaders | Function for setting HTTP headers to serve with the file. See setHeaders below. | Function |
For more information, see Serving static files in Express.
dotfiles
Possible values for this option are:
- “allow” - No special treatment for dotfiles.
- “deny” - Deny a request for a dotfile, respond with
403, then callnext(). - “ignore” - Act as if the dotfile does not exist, respond with
404, then callnext().
NOTE: With the default value, it will not ignore files in a directory that begins with a dot.
fallthrough
When this option is true, client errors such as a bad request or a request to a non-existent file will cause this middleware to simply call next() to invoke the next middleware in the stack. When false, these errors (even 404s), will invoke next(err).
Set this option to true so you can map multiple physical directories to the same web address or for routes to fill in non-existent files.
Use false if you have mounted this middleware at a path designed to be strictly a single file system directory, which allows for short-circuiting 404s for less overhead. This middleware will also reply to all methods.
setHeaders
For this option, specify a function to set custom response headers. Alterations to the headers must occur synchronously.
The signature of the function is:
fn(res, path, stat)
Arguments:
-
res, the response object. -
path, the file path that is being sent. -
stat, thestatobject of the file that is being sent.
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