> For the complete documentation index, see [llms.txt](https://frinn.gitbook.io/custom-machinery-1.21/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://frinn.gitbook.io/custom-machinery-1.21/mod-integrations/kubejs/recipes/function.md).

# Function

A function requirement is a way to execute javascript code when a recipe is processing.

To do that 2 things are needed : 

* A method that will tell the recipe to send a KubeJS event when needed.
* An event listener where the JS code will be put.

Both the recipe method and the event listener are linked using a String id.

Note: This has nothing to do with MC functions (or commands), this requirement allow you to make your own code in JavaScript and pass it to be executed by the machine.

### In the recipe

```javascript
//Executed when the machine is idle and search a recipe to process.
.requireFunctionToStart("id")

//Executed the first tick of the crafting process.
.requireFunctionOnStart("id")

//Executed each tick of the crafting process.
.requireFunctionEachTick("id")

//Executed the last tick of the crafting process.
.requireFunctionOnEnd("id")
```

* The passed id MUST be a string.
* Several functions can share the same id, but they will all share the same event too.
* The function can be delayed, put `.delay(delay)` directly after any `.requireFunctionXXX()` call to make the function be executed at the specified delay.

### In a server script (outside the recipe event)

```javascript
CustomMachineryEvents.recipeFunction("id", event => {
  //Print the machine id in logs when the function is run.
  console.info(event.machine.id)

  //Immediately stop the function and allows the recipe to run.
  event.success()
  
  //Immediately stop the function and display an error in the machine.
  event.error("Error")
})
```

* If neither `event.success()` nor `event.error()` are called the recipe will be allowed to run.
* If `event.error()` is called without specifying an error message it will show the default one instead.
* The `event` object contains several useful methods, see more on [its dedicated wiki page](/custom-machinery-1.21/mod-integrations/kubejs/recipes/function/function-event.md).

### Example :

```javascript
ServerEvents.recipes(event => {
	event.recipes.custommachinery.custom_machine("custommachinery:power_crusher", 200)
	.requireFunctionEachTick("add_2_diamonds")
})

CustomMachineryEvents.recipeFunction("add_2_diamonds", event => {
	let remaining = event.machine.addItemToSlot("output1", "2x minecraft:diamond", true)

	if(remaining.count == 0) {
                event.machine.addItemToSlot("output1", "2x minecraft:diamond", false)
		event.success()
        }
	event.error("Can't add 2 diamonds in output slot")
})
```

### Migrating from previous function requirement

Previously : 

```javascript
ServerEvents.recipes(event => {
	event.recipes.custommachinery.custom_machine("id", time)
	.requireFunctionXXX(ctx => {
		//Do code here
	})
})
```

Now : 

```javascript
ServerEvents.recipes(event => {
	event.recipes.custommachinery.custom_machine("id", time)
	.requireFunctionXXX("id")
})

CustomMachineryEvents.recipeFunction("id", event => {
  	//Do code here
  	//Use event.success() and event.error("error")
  	//instead of return ctx.success() and return ctx.error("error")
})
```


---

# Agent Instructions
This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com.

## Querying This Documentation
If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter, and the optional `goal` query parameter:

```
GET https://frinn.gitbook.io/custom-machinery-1.21/mod-integrations/kubejs/recipes/function.md?ask=<question>&goal=<endgoal>
```

`ask` is the immediate question: it should be specific, self-contained, and written in natural language.
`goal` is optional and describes the broader end goal you are ultimately trying to accomplish on behalf of the user. GitBook uses it to tailor the answer towards what is most useful for that goal.

The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.