indexOf

%dw 2.0
output application/json
---
{
  present: ["a","b","c","d"] indexOf "c",
  notPresent: ["x","w","x"] indexOf "c",
  presentMoreThanOnce: ["a","b","c","c"] indexOf "c",
}

{
   "present": 2,
   "notPresent": -1,
   "presentMoreThanOnce": 2
 }

%dw 2.0
output application/json
---
{
  present: "abcd" indexOf "c",
  notPresent: "xyz" indexOf "c",
  presentMoreThanOnce: "abcdc" indexOf "c",
}

{
   "present": 2,
   "notPresent": -1,
   "presentMoreThanOnce": 2
 }