How can I write this expression in DW 2.0 mule 4 - mule

Question

I am using this expression in TM component in mule3 and I wants to migrate this in mule 4.Can anyone please help me to solve this issue
(payload splitBy "\n") map using (startIndex = 41,lastIndex = ((sizeOf $) - 1)){
"Data" : $[[startIndex][0] .. [lastIndex][0]]
I am getting missing expression error
using() is deprecated, replace with do-block
Unable to call: splitBy with arguments: (String | Null, "\\n").
Reasons:
Expecting Type: String, but got: Null. |-- From: String |- From: splitBy(text: String, separator: String) ->
Array<String> 4| (payload splitBy "\n") map using (startIndex =
41,lastIndex = ((sizeOf $) - 1)){
^^^^^^^
Expecting Type: String, but got: Null. |-- From: String
Expecting Type: Regex, but got: "\\n". |-- From: Regex |- From: splitBy(text: String, regex: Regex) ->
Array<String> 4| (payload splitBy "\n") map using (startIndex =
41,lastIndex = ((sizeOf $) - 1)){
^^^^^^^
when I tried same expression in mule 4
Thanks In advance to all who can try to help me

Answer 1

As stated you can change your expression to use do instead of using.
The .. will be replaced by to for getting the substring
%dw 2.0
output application/json
---
(payload splitBy "\n") map do {
var startIndex = 41
var lastIndex = sizeOf($) - 1
---
{
"Data" : $[[startIndex][0] to [lastIndex][0]]
}
}
Note that [startIndex][0] is same as startIndex so you can replace $[[startIndex][0] to [lastIndex][0]] with $[startIndex to lastIndex]
Also if the startIndex is really static and do not depend on the element, you can reduce your expression with
%dw 2.0
output application/json
var startIndex = 41
---
payload
splitBy "\n"
map {
"Data" : $[startIndex to (sizeOf($) -1)]
}