Debugging Express

To see all the internal logs used in Express, set the DEBUG environment variable to express:* when launching your app.

Terminal window

$DEBUG=express:*nodeindex.js

On Windows, use the corresponding command.

Terminal window

> $env:DEBUG = "express:*"; nodeindex.js

Running this command on the default app generated by the express generator prints the following output:

Terminal window

$DEBUG=express:*node./bin/www
express:router:routenew/+0ms
express:router:layernew/+1ms
express:router:routeget/+1ms
express:router:layernew/+0ms
express:router:routenew/+1ms
express:router:layernew/+0ms
express:router:routeget/+0ms
express:router:layernew/+0ms
express:applicationcompileetagweak+1ms
express:applicationcompilequeryparserextended+0ms
express:applicationcompiletrustproxyfalse+0ms
express:applicationbootingindevelopmentmode+1ms
express:routeruse/query+0ms
express:router:layernew/+0ms
express:routeruse/expressInit+0ms
express:router:layernew/+0ms
express:routeruse/favicon+1ms
express:router:layernew/+0ms
express:routeruse/logger+0ms
express:router:layernew/+0ms
express:routeruse/jsonParser+0ms
express:router:layernew/+1ms
express:routeruse/urlencodedParser+0ms
express:router:layernew/+0ms
express:routeruse/cookieParser+0ms
express:router:layernew/+0ms
express:routeruse/stylus+90ms
express:router:layernew/+0ms
express:routeruse/serveStatic+0ms
express:router:layernew/+0ms
express:routeruse/router+0ms
express:router:layernew/+1ms
express:routeruse/usersrouter+0ms
express:router:layernew/users+0ms
express:routeruse/ &lt;anonymous&gt; +0ms
express:router:layernew/+0ms
express:routeruse/ &lt;anonymous&gt; +0ms
express:router:layernew/+0ms
express:routeruse/ &lt;anonymous&gt; +0ms
express:router:layernew/+0ms

When a request is then made to the app, you will see the logs specified in the Express code:

Terminal window

express:routerdispatchingGET/+4h
express:routerquery:/+2ms
express:routerexpressInit:/+0ms
express:routerfavicon:/+0ms
express:routerlogger:/+1ms
express:routerjsonParser:/+0ms
express:routerurlencodedParser:/+1ms
express:routercookieParser:/+0ms
express:routerstylus:/+0ms
express:routerserveStatic:/+2ms
express:routerrouter:/+2ms
express:routerdispatchingGET/+1ms
express:viewlookup"index.pug"+338ms
express:viewstat"/projects/example/views/index.pug"+0ms
express:viewrender"/projects/example/views/index.pug"+1ms

To see the logs only from the router implementation, set the value of DEBUG to express:router. Likewise, to see logs only from the application implementation, set the value of DEBUG to express:application, and so on.

Applications generated by `express`

An application generated by the express command uses the debug module and its debug namespace is scoped to the name of the application.

For example, if you generated the app with $ express sample-app, you can enable the debug statements with the following command:

Terminal window

$DEBUG=sample-app:*node./bin/www

You can specify more than one debug namespace by assigning a comma-separated list of names:

Terminal window

$DEBUG=http,mail,express:*nodeindex.js

Advanced options

When running through Node.js, you can set a few environment variables that will change the behavior of the debug logging:

Name	Purpose
`DEBUG`	Enables/disables specific debugging namespaces.
`DEBUG_COLORS`	Whether or not to use colors in the debug output.
`DEBUG_DEPTH`	Object inspection depth.
`DEBUG_FD`	File descriptor to write debug output to.
`DEBUG_SHOW_HIDDEN`	Shows hidden properties on inspected objects.

Note

The environment variables beginning with DEBUG_ end up being converted into an Options object that gets used with %o/%O formatters. See the Node.js documentation for util.inspect() for the complete list.

Debugging Express

Applications generated by express

Advanced options

Note

Applications generated by `express`