DataWeave 2.2 is compatible and bundled with Mule 4.2. Standard Support for Mule 4.2 ended on May 2, 2021, and this version of Mule will reach its End of Life on May 2, 2023, 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.

prependIfMissing(String, String): String

Prepends the prefix to the beginning of the string if the text does not already start with that prefix.

Introduced in DataWeave 2.2.0. Supported by Mule 4.2 and later.


Name Description


The input string.


The text to use as prefix.


This example shows how prependIfMissing behaves with different inputs and sizes.


%dw 2.0
import prependIfMissing from dw::core::Strings
output application/json
  "a": prependIfMissing(null, ""),
  "b": prependIfMissing("abc", ""),
  "c": prependIfMissing("", "xyz"),
  "d": prependIfMissing("abc", "xyz"),
  "e": prependIfMissing("xyzabc", "xyz")


  "a": null,
  "b": "abc",
  "c": "xyz",
  "d": "xyzabc",
  "e": "xyzabc"

prependIfMissing(Null, String): Null

Helper function to make prependIfMissing work with null value.

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