`log()`

Output a log message in the query summary and return null.

Signature

log(args: ...Any) => Null

Description

The log() method outputs args containing a message to the summary of query responses. In the summary, log messages are annotated as info.

log() is similar to console.log() or print() in other programming languages.

`log()` and `dbg()`

log() is similar to dbg() except that log() does not return its message in the query results.

Log message template

The log message template is:

info at *<source>*:<line>: <message>

where:

Field Description

<source>

Message source.
One of:

Source Description

query

The log() call occurred in the main query body.

udf:<function>

The log() call occurred in the user-defined function named <function>

<line>

Line number where log() is used.

<message>

String-serialized message.

Log messages for UDF calls

When calling a user-defined function (UDF) that uses log(), the visibility of log messages depends on the authentication secret's role:

Role Visibility

Role	Visibility
`admin`, `server`	Messages are returned in the response’s `summary`.
`server-readonly`, User-defined role	Messages are not returned, even if the UDF is annotated with `@role(admin)` or `@role(server)`.

admin, server

Messages are returned in the response’s summary.

server-readonly, User-defined role

Messages are not returned, even if the UDF is annotated with @role(admin) or @role(server).

Parameters

Parameter Type Required Description

Parameter	Type	Required	Description
`args`	Any		Values to output to the query summary. Supports interpolated strings containing FQL variables.

args

Any

Values to output to the query summary. Supports interpolated strings containing FQL variables.

Return value

Type	Description
Null	After output, the `args` are discarded.

Examples

The following FQL query logs several summary messages:

log("Before assignment")
let x = 5
let y = { lat: 37.5542782, long: -122.3007394 }
log("After assignment x=#{x}")
log(y)
x

The query as a Query endpoint request:

 curl -X POST \
  'https://db.fauna.com/query/1' \
  -H 'Authorization: Bearer <FAUNA_SECRET>' \
  -H 'Content-Type: application/json' \
  -H 'X-Format: tagged' \
  -d '{
    "query": "log(\"Before assignment\")\nlet x = 5\nlet y = { lat: 37.5542782, long: -122.3007394 }\nlog(\"After assignment x=#{x}\")\nlog(y)\nx\n"
  }'

Unlike dbg(), log() does not return a value. The message is excluded from the query results in data.

The summary includes the query lines that called log():

{
  "data": {
    "@int": "5"
  },
  "static_type": "5",
  "summary": "info at *query*:1: Before assignment\n\ninfo at *query*:4: After assignment x=5\n\ninfo at *query*:5: { lat: 37.5542782, long: -122.3007394 }",
  ...
}

When unescaped, the response’s summary renders as:

"info at *query*:1: Before assignment

info at *query*:4: After assignment x=5

info at *query*:5: { lat: 37.5542782, long: -122.3007394 }

log()