[[transform-script]]
=== Script Transform

A <<transform, Transform>> that executes a script on the current payload in the
watch execution context and replaces it with a newly generated one. The following
snippet shows how a simple script transform can be defined on the watch level:

TIP:  The `script` transform is often useful when used in combination with the
      <<transform-search, `search`>> transform, where the script can extract only
      the significant data from a search result, and by that, keep the payload
      minimal. This can be achieved with the <<transform-chain, `chain`>>
      transform.


[source,js]
--------------------------------------------------
{
  "transform" : {
    "script" : "return [ 'time' : ctx.trigger.scheduled_time ]" <1>
  }
}
--------------------------------------------------
<1> A simple `painless` script that creates a new payload with a single `time`
    field holding the scheduled time.

NOTE: The executed script may either return a valid model that is the equivalent
      of a Java(TM) Map or a JSON object (you will need to consult the
      documentation of the specific scripting language to find out what this
      construct is). Any other value that is returned will be assigned and
      accessible to/via the `_value` variable.

The `script` attribute may hold a string value in which case it will be treated
as an inline script and the default elasticsearch script languages will be assumed
(as described in {ref}/modules-scripting.html#modules-scripting[here]). You can
use the other scripting languages supported by Elasticsearch. For this, you need
to set the `script` field to an object describing the script and its language.
The following table lists the possible settings that can be configured:

[[transform-script-settings]]
.Script Transform Settings
[options="header,footer"]
|======
| Name      |Required | Default    | Description

| `inline`  | yes*    | -          | When using an inline script, this field holds
                                     the script itself.

| `id`      | yes*    | -          | When referring to a stored script, this
                                     field holds the id of the script.

| `lang`    | no      | `painless` | The script language

| `params`  | no      | -          | Additional parameters/variables that are
                                     accessible by the script

|======

When using the object notation of the script, one (and only one) of `inline`,
or `id` fields must be defined

NOTE: In addition to the provided `params`, the scripts also have access to the
      <<watch-execution-context, Standard Watch Execution Context Parameters>>.