AWS StepFunctions: prefix input string

Question

Using TypeScript and CDK, how do I define a task that prefixes one of the fields of the input and keeps the rest unchanged?

Input:

{
  "field1": "foo",
  "field2": "bar"
}

Expected output:

{
  "field1": "baz_foo",
  "field2": "bar"
}

Answer 1

This can be done with a Pass task and intrinsic function States.Format.

  const addPrefix = new sfn.Pass(this, 'AddPrefix', {
    parameters: {
      'field1.$': "States.Format('{}{}', 'baz_', $.field1)",
      'field2.$': '$.field2',
    },
  });