log

log(String, T): T

Without changing the value of the input, log returns the input as a system log.

Use this function to help with debugging DataWeave scripts. A Mule app outputs the results through the DefaultLoggingService, which you can see in the Studio console.

Parameters

Name Description

Name	Description
`prefix`	An optional string that typically describes the log.
`value`	The value to log.

prefix

An optional string that typically describes the log.

value

The value to log.

Example

This example logs the specified message. Note that the DefaultLoggingService in a Mule app that is running in Studio returns the message WARNING - "Houston, we have a problem," adding the dash - between the prefix and value. The Logger component’s LoggerMessageProcessor returns the input string "Houston, we have a problem.", without the WARNING prefix.

Source

%dw 2.0
output application/json
---
log("WARNING", "Houston, we have a problem.")

Console Output

WARNING - "Houston, we have a problem."

Expression Output

"Houston, we have a problem."

Example

This example shows how to log the result of expression myUser.user without modifying the original expression myUser.user.friend.name.

Source

%dw 2.0
output application/json

var myUser = {user: {friend: {name: "Shoki"}, id: 1, name: "Tomo"}, accountId: "leansh" }
---
log("User", myUser.user).friend.name

Console Output

 User - {
   friend: {
     name: "Shoki"
   },
   id: 1,
   name: "Tomo"
 }

Expression Output

"Shoki"