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You can specify debug strings when you run an application, as explained below, to display specific log output to the console. You can also redirect the output to a file, if desired. These techniques are often helpful in debugging applications.

Using debug strings

LoopBack has a number of built-in debug strings to help with debugging. Specify a string on the command-line via an environment variable as follows:

MacOS and Linux

$ DEBUG=<pattern>[,<pattern>...] npm start

Windows

C:\> set DEBUG=<pattern>[,<pattern>...]
C:\> npm start

where <pattern> is a string-matching pattern specifying debug strings to match. You can specify as many matching patterns as you wish.

For example (MacOS and Linux):

$ DEBUG=loopback:datasource npm start

Or, on Windows:

C:\> set DEBUG=loopback:datasource
C:\> npm start

You’ll see output such as (truncated for brevity):

loopback:datasource Settings: {"name":"db","debug":true} -0ms
loopback:datasource Settings: {"name":"geo","connector":"rest",...

You can use an asterisk  (*) in the pattern to match any string. For example the following would match any debug string containing “oracle”:

$ DEBUG=*oracle npm start

You can also exclude specific debuggers by prefixing them with a “-“ character. For example, DEBUG=*,-rest-crud:* would include all debuggers except those starting with “rest-crud:”.

Debug string format

These strings have the format

module[:area]:string

Where:

  • module is the name of the module, for example loopback or loopback-connector-mongodb.
  • area is an optional identifier such as cli or repository to identify the purpose of the module
  • string is the debug string specified in the target TypeScript/JavaScript source file, such as application.ts.

For example:

loopback:cli:model-generator

The debug string model-generator is specified in the source file generators/model/index.js of the @loopback/cli module.

Debug strings reference

Module Source file String
@loopback
@loopback/authorization src/authorize-interceptor.ts loopback:authorization:interceptor
@loopback/boot src/bootstrapper.ts loopback:boot:bootstrapper
src/booters/interceptor.booter.ts loopback:boot:interceptor-booter
src/booters/lifecycle-observer.booter.ts loopback:boot:lifecycle-observer-booter
src/booters/model-api.booter.ts loopback:boot:model-api
src/booters/service.booter.ts loopback:boot:service-booter
@loopback/booter-lb3app src/lb3app.booter.ts loopback:boot:lb3app
@loopback/cron src/cron.component.ts loopback:cron
@loopback/rest-crud src/crud-rest-builder.ts loopback:boot:crud-rest
@loopback/cli please check each generator loopback:cli:_string_
@loopback/context src/interceptor.ts loopback:context:interceptor
src/binding.ts loopback:context:bindging
src/context-view.ts loopback:context:view
src/invocation.ts loopback:context:invocation
src/interceptor-chain.ts loopback:context:interceptor-chain
@loopback/http-caching-proxy src/http-caching-proxy.ts loopback:http-caching-proxy
@loopback/core src/lifecycle-registry.ts loopback:core:lifecycle
src/application.ts loopback:core:application
@loopback/openapi-v3 src/* loopback:openapi
@loopback/repository src/relations/belongs-to/belongs-to-accessor.ts loopback:repository:belongs-to-accessor
src/relations/has-many/has-many-repository-factory.ts loopback:repository:has-many-repository-factory
src/relations/has-one/has-one-repository-factory.ts loopback:repository:has-one-repository-factory
@loopback/repository-json-schema src/build-schema.ts loopback:repository-json-schema:build-schema
@loopback/rest src/rest-server/ loopback:rest:server
src/sequence.ts loopback:rest:sequence
loopback-datasource-juggler
lib/datasource.js loopback:datasource
Connectors
loopback-connector lib/connector.js loopback:connector
loopback-connector-cassandra lib/cassandra.js loopback:connector:cassandra
loopback-connector-cloudant lib/cloudant.js loopback:connector:cloudant
loopback-connector-couchdb2 lib/couchdb2.js loopback:connector:couchdb2
loopback-connector-dashdb lib/dashdb.js loopback:connector:dashdb
loopback-connector-db2 lib/db2.js loopback:connector:db2
loopback-connector-ibmi lib/ibmiconnector.js loopback:connector:ibmiconnector
loopback-connector-kv-redis lib/kv-redis.js loopback:connector:kv-redis
loopback-connector-mongodb lib/mongodb.js loopback:connector:mongodb
loopback-connector-mssql lib/mssql.js loopback:connector:mssql
loopback-connector-mysql lib/mysql.js loopback:connector:mysql
loopback-connector-oracle lib/oracle.js loopback:connector:oracle
loopback-connector-postgresql lib/postgresql.js loopback:connector:postgresql
loopback-connector-rest lib/rest-builder.js loopback:connector:rest
lib/rest-connector.js loopback:connector:rest
lib/rest-model.js loopback:connector:rest
lib/swagger-client.js loopback:connector:rest:swagger
loopback-connector-soap lib/soap-connector.js loopback:connector:soap