Freshdesk Webhook - Get data from subject to populate a custom field

Question

Has anyone tried to get a string from a ticket subject and populate a custom field using Webhooks on Freshdesk?

I am trying to get a reservation number that starts with the letter 'R' and put it on a custom field.

Example code:

     <script>
var strng;  
    strng = "Either way, time largely defines the human experience.";  
    var incStr = strng.includes("human");  
    document.write("Is 'human' present in the string? : " + incStr);
</script>

{
"custom_fields": {"Resv#": incStr}

}

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