Define DataWeave Functions

Standard Support for Mule 4.1 ended on November 2, 2020, and this version of Mule will reach its End of Life on November 2, 2022, when Extended Support ends.

Deployments of new applications to CloudHub that use this version of Mule are no longer allowed. Only in-place updates to applications are permitted.

MuleSoft recommends that you upgrade to the latest version of Mule 4 that is in Standard Support so that your applications run with the latest fixes and security enhancements.

You can define your own DataWeave functions using the fun declaration in the header of a DataWeave script. For example, this a simple DataWeave function accepts a single String argument that outputs "HELLO":

%dw 2.0
output application/json
fun toUpper(aString) = upper(aString)
---
toUpper("hello")

The argument to a DataWeave function can be any DataWeave expression. This function also outputs "HELLO":

%dw 2.0
output application/json
fun toUpper(aString) = upper(aString)
---
toUpper("h" ++ "el" ++ lower("LO") )

To test the type of the argument passed into your function, you can perform pattern matching with the built-in match operation.

Example: Function that Uses Pattern Matching
%dw 2.0
output application/json
fun toUpper(aString)
= aString match {
  case is String -> upper(aString)
  else -> null
}
---
toUpper("h" ++ "el" ++ lower("LO") )

This example creates a function that reformats a numeric string into a common phone number format:

Example: toPhoneFormat() Function
%dw 2.0
output application/json
fun toPhoneFormat(str: String) =
    "(" ++ str[0 to 2] ++ ") " ++ str[3 to 5] ++ "-" ++ str[6 to 9]
---
toPhoneFormat("1234567890")
Output of toPhoneFormat("1234567890")
"(123) 456-7890"

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