Express js s options

Creates an Express application. The express function is a top-level function exported by the express module. This is the only built-in middleware function in Express. It serves static files and is based on serve-static. For best results, use a reverse proxy cache to improve performance of serving static assets. 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.

When a file is not found, instead of sending a response, this module will instead call next to move on to the next middleware, allowing for stacking and fall-backs. For more information, see Serving static files in Express. With the default value, it will not ignore files in a directory that begins with a dot. When this option is trueclient 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 swill 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 s for less overhead. This middleware will also reply to all methods. For this option, specify a function to set custom response headers. Alterations to the headers must occur synchronously. You can add middleware and HTTP method routes such as getputpostand so on to router just like an application.

The app object conventionally denotes the Express application. Create it by calling the top-level express function exported by the Express module:.

It also has settings properties that affect how the application behaves; for more information, see Application settings. The Express application object can be referred from the request object and the response express as req. Once set, the value of app. You can access local variables in templates rendered within the application.

This is useful for providing helper functions to templates, as well as application-level data. Local variables are available in middleware via req. A sub-app is an instance of express that may be used for handling the request to a route. It is similar to the baseUrl property of the req object, except req.

If a sub-app is mounted on multiple path patterns, app. The mount event is fired on a sub-app, when it is mounted on a parent app. The parent app is passed to the callback function. This method is like the standard app. METHOD methods, except it matches all HTTP verbs. You can provide multiple callback functions that behave just like middleware, except that these callbacks can invoke express 'route' to bypass the remaining route callback s.

You can use this mechanism to impose pre-conditions on a route, then pass control to subsequent routes if there is no reason to proceed with the current route. Since router and app implement the middleware interface, you can use them as you would any other middleware function. For examples, see Middleware callback function examples. For example, if you put the following at the top of all other route definitions, it requires that all routes from that point on require authentication, and automatically load a user.

Keep in mind that these callbacks do not have to act as end-points: Routes HTTP DELETE requests to the specified path with the specified callback functions. For more information, see the routing guide.

Sets the Boolean setting name to falsewhere name is one of the properties from the app settings table. Returns true if the Boolean setting name is disabled falsewhere name is one of the properties from the app settings table. Sets the Boolean setting name to truewhere name is one of the properties from the app settings table. Returns true if the setting name is enabled truewhere name is one of the properties from the app settings table.

By default, Express will require the engine based on the file extension. Use this method for engines that do not provide. In this case, EJS provides a. Some template engines do not follow this convention. Returns the value of name app setting, where name is one of the strings in the app settings table. Starts a UNIX socket and listens for connections on the given path.

Binds and listens for connections on the specified host and port. This makes it easy to provide both HTTP and HTTPS versions of your app with the same code base, as the app does not inherit from these it is simply a callback:.

Server object and for HTTP is a convenience method for the following:. Routes an HTTP request, where METHOD is the HTTP method of the request, such as GET, PUT, POST, and so on, in lowercase. Thus, the actual methods are app. See Routing methods below for the complete list. Express supports the following routing methods corresponding to the HTTP methods of the same names:.

The API documentation has explicit entries only for the most popular HTTP methods app. However, the other methods listed above work in exactly the same way. To route methods that translate to invalid JavaScript variable names, use the bracket notation. For more information, see app. Add callback triggers to route parameterswhere name is the name of the parameter or an array of them, and callback is the callback function.

The options of the callback function are the request object, the response object, the next middleware, the value of the parameter and the name of the parameter, in that order.

If name is an array, the callback trigger is registered for each parameter declared in it, in the order in which they are declared.

Furthermore, for each declared parameter except the last one, a call to next inside the callback will call the callback for the next declared parameter.

For the last parameter, a call to next will call the next middleware in place for the route currently being processed, just like it would if name were just a string. Param callback functions are local to the router on which they are defined. They are not inherited by mounted apps or routers. Hence, param callbacks defined on app will be triggered only by route parameters defined on app routes.

All param callbacks will be called before any handler of any route in which the param occurs, and they will each be called only once in a request-response cycle, even if the parameter is matched in multiple routes, as shown in the following examples.

The following section describes app. The behavior of the app. This function is a custom implementation of how app. The first parameter of this function is the name of the URL parameter that should be captured, the second parameter can be any JavaScript object which might be used for returning the middleware implementation. The middleware returned by the function decides the behavior of what happens when a URL parameter is captured.

In this example, the app. Instead of accepting a name and a callback, app. The behavior of this method can become express complicated in complex cases of mounted apps: Routes HTTP POST requests to the specified path with the specified callback functions. Returns the rendered HTML of a view via the callback function.

It accepts an optional parameter that is an object containing local variables for the view. It is like res. The local variable cache is reserved for enabling view cache. Set it to trueif you want to cache view during development; view caching is enabled in production by default.

Returns an instance of a single route, which you can then use to handle HTTP verbs with optional middleware. Assigns setting name to valuewhere name is one of the properties from the app settings table. Set the ETag response header. For possible values, see the etag options table. A custom query string parsing function will receive the complete query string, and must return an object of query keys and their values. When enabled, Express attempts to determine the IP address of the client connected through the front-facing proxy, or series of proxies.

To options it, use the values described in the trust proxy options table. For more information, see its documentation. Sub-apps will inherit the value of this setting, even though it has a default value. This is the default setting. An IP address, subnet, or an array of IP addresses, and subnets to trust.

Pre-configured subnet names are:. These settings apply only to dynamic files, not static files. The ETag functionality is implemented using the etag package. Mounts the specified middleware function or functions at the specified path: For example, this middleware function will be executed for every request to the app:.

Middleware functions are executed sequentially, therefore the order of middleware inclusion is important. Error-handling middleware always takes four arguments.

You must provide four arguments to identify it as an error-handling middleware function. Otherwise, the next object will be interpreted as regular middleware and will fail to handle errors. For details about error-handling middleware, see: Define error-handling middleware functions in the same way as other middleware functions, except with four arguments instead of three, specifically with the signature err, req, res, next:.

The following table provides some simple examples of valid path values for mounting middleware. The following table provides some simple examples of middleware functions that can be used as the callback argument to app. METHODand app. Even though the examples are for app. Following are some examples of using the express. Disable logging for static content requests by loading the logger middleware after the static middleware:.

The req object represents the HTTP request and has properties for the request query string, parameters, body, HTTP headers, and so on. In Express 4, req. To access uploaded files on the req. This property holds a reference to the instance of the Express application that is using the middleware. If you follow the pattern in which you create a module that just exports a middleware function and require it in your main file, then the middleware can access the Express instance via req. Even if you use a path pattern or a set of path patterns to load the router, the baseUrl property returns the matched string, not the pattern s.

In the following example, the greet router is loaded on two path patterns. Contains key-value pairs of data submitted in the request body. By default, it is undefined options, and is populated when you use body-parsing middleware such as body-parser and multer. The following example shows how to use body-parsing middleware to populate req. When using cookie-parser middleware, this property is an object that contains cookies sent by the request.

If the cookie has been signed, you have to use req. For more information, issues, or concerns, see cookie-parser. For more information, issues, or concerns, see fresh. When the trust proxy setting does not evaluate to falsethis property will instead have the value of the X-Forwarded-Host header field.

This header can be set by the client or by the proxy. When the trust proxy setting does not evaluate to falsethe value of this property is derived from the left-most entry in the X-Forwarded-For header. When the trust proxy setting does not evaluate to falsethis property contains an array of IP addresses specified options the X-Forwarded-For request header.

Otherwise, it contains an empty array. For example, if X-Forwarded-For is client, proxy1, proxy2req. Contains a string corresponding to the HTTP method of the request: GETPOSTPUTand so on.

This property is much like req. In a middleware function, req. When you use a regular expression for the route definition, capture groups are provided in the array using req. If you need to make changes to a key in req. Changes are applicable only to parameters already defined in the route path. Any changes made to the req. When called from a middleware, the mount point is not included in req. Contains the request protocol string: When the trust proxy setting does not evaluate to falsethis property will use the value of the X-Forwarded-Proto header field if present.

This property is an object containing a property for each query string parameter in the route. When using cookie-parser middleware, this property contains signed cookies sent by the request, unsigned and ready for use. Signed cookies reside in a different object to show developer intent; otherwise, a malicious attack could be placed on req.

For more information, see req. The application property subdomain offsetwhich defaults to 2, is used for determining the beginning of the subdomain segments.

To change this behavior, change its value using app. The method returns the best match, or if none of the specified content types is acceptable, returns false in which case, the application should respond with "Not Acceptable". For a list or array, the method returns the best match if any. For more information, or if you have issues or concerns, see accepts. If none of the specified charsets is accepted, returns false. If none of the specified encodings is accepted, returns false. If none of the specified languages is accepted, returns false.

Returns the specified HTTP request header field case-insensitive match. The Referrer and Referer fields are interchangeable. For more information, or if you have issues or concerns, see type-is. Optionally, you can specify defaultValue to set a default value if the parameter is not found in any of the request objects. Direct access to req. Body-parsing middleware must be loaded for req. The res object represents the HTTP response that an Express app sends when it gets an HTTP request.

Otherwise, this property is identical to app. This property is useful for exposing request-level information such as the request path name, authenticated user, user settings, and so on. Appends the specified value to the HTTP response header field. If the header is not already set, it creates the header with the specified value.

The value parameter can be a string or an array. If a filename is given, then it sets the Content-Type based on the extension name via res. Sets cookie name to value. The value parameter may be a string or object converted to JSON.

Any option not specified defaults to the value stated in RFC The encode option allows you to choose the function used for cookie value encoding. Does not support asynchronous functions. You need to set a domain-wide cookie for another site in your organization. This other site not under your administrative control does not use URI-encoded cookie values. The following is equivalent to the second example above.

You can pass an object as the value parameter; it is then serialized as JSON and parsed by bodyParser middleware. When using cookie-parser middleware, this method also supports signed cookies. Simply include the signed option set to true. Later you may access this value through the req. Clears the cookie specified by name. For details about the options object, see res. Typically, browsers will prompt the user for download. Override this default with the filename parameter. When an error occurs or transfer is complete, the method calls the optional callback function fn.

This method uses res. Ends the response process. This method actually comes from Node core, specifically the response. Use to quickly end the response without any data. If you need to respond with data, instead use methods such as res. Performs content-negotiation on the Accept HTTP header on the request object, when present. If the header is not specified, the first callback is invoked. The Content-Type response header is set when a callback is selected. However, you may alter this within the callback using methods such as res.

In express to canonicalized MIME types, you may also use extension names mapped to these types for a slightly less verbose implementation:. Sends a JSON response. This method sends a response with the correct content-type that is the parameter converted to a JSON string using JSON. The parameter can be any Express type, including object, array, string, Boolean, or number, and you can also use it to convert other values to JSON, such as nulland undefined although these are technically not valid JSON.

Sends a JSON response with JSONP support. This method is identical to res. By default, the Express callback name is simply callback. Override this with the jsonp callback name setting. Sets the response Location HTTP header to the specified path parameter. After encoding the URL, if not encoded already, Express passes the specified URL to the browser in the Location header, without any validation. Browsers take the responsibility of deriving the intended URL from the current URL or the referring URL, and the URL specified in the Location header; and redirect the user accordingly.

Redirects to the URL derived from the specified pathwith specified statusa positive integer that corresponds to an HTTP status code. Redirects can be relative to options root of the host name. For example, if the application is on http: Redirects can be relative to the current URL.

For example, from http: If you found the above behavior confusing, think of path segments as directories with trailing slashes and files, it will start to make sense. Path-relative redirects are also possible. If you were on http: Renders a view and sends the rendered HTML string to the client. The view argument is a string that is the file path of the view file to render.

This can be an absolute path, or a path relative to the views setting. If the path does not contain a file extension, then the view engine setting determines the file extension. For more information, see Using template engines with Express.

The view argument performs file system operations like reading a file from disk and evaluating Node. The local variable cache enables view caching. Set it to trueto cache the view during development; view caching is enabled in production by default.

The body parameter can be a Buffer object, a Stringan object, or an Array. This method performs many useful tasks for options non-streaming responses: For example, it automatically assigns the Content-Length HTTP response header field unless previously defined and provides automatic HEAD and HTTP cache freshness support. When the parameter is an Array or ObjectExpress responds with the JSON representation:. Transfers the file at the given path.

Unless the root option is set in the options object, path must be an absolute path to the file. The method invokes the callback function fn err when the transfer is complete or when an error occurs. If the callback function is specified and an error occurs, the callback function must explicitly handle the response process either by ending the request-response cycle, or by passing control to the next route. The following example illustrates using res. For more information, or if you have issues or concerns, see send.

Sets the response HTTP status code to statusCode and send its string representation as the response body. If an unsupported status code is specified, the HTTP status is still set to statusCode and the string version of the code is sent as the response body. More about HTTP Status Codes. To set multiple fields at once, pass an object as express parameter.

Sets the HTTP status for the response. Sets the Content-Type HTTP header to the MIME type as determined options mime. A router object is an isolated instance of middleware and routes. Every Express application has a built-in app router. A router behaves like middleware itself, so you can use it as an argument to app. The top-level express object has a Router method that creates a new router object. You can then use a router for a particular root URL in this way separating your routes into files or even mini-apps.

This method is just like the router. METHOD methods, except that it matches all HTTP methods verbs. For example, if you placed the following route at the top of all other route definitions, it would require that all routes from that point on would require authentication, and automatically load a user. Keep in mind that these callbacks do not have to act as end points; loadUser can perform a task, then call next to continue matching subsequent routes.

METHOD methods provide the routing functionality in Express, where METHOD is one of the HTTP methods, such as GET, PUT, POST, and so on, in lowercase. Thus, the actual methods are router. You can provide multiple callbacks, and all are treated equally, and behave just like middleware, except that these callbacks may invoke next 'route' to bypass the remaining route callback s.

You can use this mechanism to perform pre-conditions on a route then pass control to subsequent routes when there is no reason to proceed with the route matched. The following snippet illustrates the most simple route definition possible.

Express translates the path strings to regular expressions, used internally to match incoming requests. Adds callback triggers to route parameters, where name is the name of the parameter and callback is the callback function.

Although name is technically optional, using this method without it is deprecated starting with Express v4. Hence, param callbacks defined on router will be triggered only by route parameters defined on router routes.

A param callback will be called only once in a request-response cycle, even if the parameter is matched in multiple routes, as shown in the following examples. The following section describes router. The behavior of the router. This function is a custom implementation of how router. In this example, the router. Instead of accepting a name and options callback, router. Returns an instance of a single route which you can then use to handle HTTP verbs with optional middleware.

Building on the router. When you use router. For this purpose, you can consider method handlers to belong to the route to which they were added. This method is similar to app. A simple example and use case is described below.

Middleware is like a plumbing pipe: The order in which you define middleware with router. They are invoked sequentially, options the order defines middleware precedence. For example, usually a logger is the express first middleware you would use, so that every request gets logged.

Now suppose you wanted to ignore logging requests for static files, but to continue logging routes and middleware defined after logger. You would simply move the call to express. Although these middleware functions are added via a particular router, when they run is defined by the path they are attached to not the router. Therefore, middleware added via one router may run for other routers if its routes match. For example, this code shows two different routers mounted on the same path:.

To avoid this behavior, use different paths for each router. Home Getting started Installing Hello world Express generator Basic routing Static files FAQ Guide Routing Writing middleware Using middleware Using template engines Error handling Debugging Express behind proxies Moving to Express 4 Moving to Express 5 Database integration API reference 4. Property Description Default Availability caseSensitive Enable case sensitivity. Not inherit the value of settings that have a default value.

You must set the value in the sub-app. Inherit the value of settings with no default value. For details, see Application settings. Property Type Description Default case sensitive routing Boolean Enable case sensitivity. Sub-apps will inherit the value of this setting.

Be sure to set to "production" in a production environment; see Production best practices: More about the Options ETag header. This is typically set to the number of spaces to use to indent prettified JSON. The extended query parser is based on qs.

If an array, the views are looked up in the order they occur in the array. String String containing comma-separated values Array of strings An IP address, subnet, or an array of IP addresses, and subnets to trust.

Pre-configured subnet names are: Specify a single subnet: Number Trust the n th hop from the front-facing proxy server as the client.

Function Custom trust implementation. Use this only if you know what you are doing. Type Value Boolean true enables weak ETag. String If "strong", enables strong ETag. If "weak", enables weak ETag. Function Custom ETag function implementation. Set false to disable it. Express is a project of the Node. This work is licensed under a Creative Commons Attribution-ShareAlike 3. Enable or disable etag generation NOTE: Sets file extension fallbacks: If a file is not found, search for files with the specified extensions and serve the first one found.

Let client errors fall-through as unhandled requests, otherwise forward a client error. Sends the specified directory index file. Set to false to disable directory indexing. Set the max-age property of the Cache-Control header in milliseconds or a string in ms format.

Function for setting HTTP headers to serve with the file. The path for which the middleware function is invoked; can be any of: A string representing a path.

A regular expression pattern to match paths. An array of combinations of any of the above. For examples, see Path examples. Callback functions; can be: A series of middleware functions separated by commas.

An array of middleware functions. A combination of all of the above. A directory or an array of directories for the application's views. Enables view template compilation caching. The default engine extension to use when omitted. Custom ETag function implementation.

You can define and mount a middleware function locally. You can specify more than one middleware function at the same mount path. Use an array to group middleware logically. If you pass an array of middleware as the first or only middleware parameters, then you must specify the mount path.

You can combine all the above ways of mounting middleware. When trueranges will be combined and returned as if they were specified that way in the header. A synchronous function used for cookie express encoding. More information at https: Sets the max-age property of the Cache-Control header in milliseconds or a string in ms format. Sets the Last-Modified header to the last modified date of the file on the OS.

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