Setting debug strings

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

The LoopBack framework 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>...] node .

Windows

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

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):

$ DEBUG=loopback:datasource node .

Or, on Windows:

C:\> set DEBUG=loopback:datasource
C:\> node .

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 node .

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

Debug string format

These strings have the format

module[:area]:fileName

Where:

• module is the name of the module, for example loopback or loopback-connector-rest.
• area is an optional identifier such as security or connector to identify the purpose of the module
• fileName is the name of the JavaScript source file, such as oracle.js.

For example:

loopback:security:access-context

identifies the source file access-context.js in the loopback module (used for security features).

Debug strings reference