---
modificationDate: August 10, 2026
title: Custom functions in EAS Workflows
description: Learn how to define reusable step sequences with custom functions.
---

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# Custom functions in EAS Workflows

Learn how to define reusable step sequences with custom functions.

Custom functions define reusable step sequences for custom jobs and hooks. You can call them with a relative path using [`uses`](/eas/workflows/syntax.md#jobsjob_idstepsstepuses), like built-in functions. Each custom function defines its steps under `runs.steps` in a **function.yml** or **function.yaml** file. These steps use the same format as [custom job steps](/eas/workflows/syntax.md#custom-jobs).

For the **function.yml** schema, see [Custom functions](/eas/workflows/syntax.md#custom-functions) in the syntax reference.

## How it works

Create a directory for your custom function with a **function.yml** file inside it. EAS Workflows also accepts **function.yaml**. EAS Workflows resolves the path you pass to `uses` relative to your EAS project directory:

`my-app`

 `.eas`

  `workflows`

   `publish-preview-update.yml`

  `functions`

   `setup`

    `function.yml`

 `eas.json`

The **.eas/functions/<name>** path in the example above is only one option. The `uses` value must start with `./` or `../` and point to a directory containing a **function.yml** or **function.yaml** file. A path that starts with `../` can point outside the EAS project directory, but the custom function must remain within the repository.

A relative `working_directory` on a step inside the custom function resolves from the job's default working directory, not the directory containing **function.yml**.

You can use custom functions in:

-   Custom job [`steps`](/eas/workflows/syntax.md#jobsjob_idsteps)
-   Build job [`steps`](/eas/workflows/syntax.md#jobsjob_idsteps)
-   Job [`hooks`](/eas/workflows/syntax.md#jobsjob_idhooks) and [`defaults.hooks`](/eas/workflows/syntax.md#defaultshooks)

## Inputs, outputs and scope

Pass inputs at the call site with `with:`. Inside the function, read an input with `${{ inputs.<name> }}`.

Define function outputs with `outputs` in **function.yml**. EAS Workflows exposes each output as a string. Read outputs as `${{ steps.<call_id>.outputs.<name> }}`. Use the `id` from the call step. The caller cannot reference the function's internal step identifiers.

Expressions use the following scopes:

-   Inside the function, `steps.*` references resolve against the function's own steps.
-   EAS Workflows evaluates the call step's `with`, `env`, and `if` values in the caller's scope.
-   Every step in the function inherits the call step's `env` values. In nested calls, inner values override outer values with the same name.
-   EAS Workflows evaluates input defaults and expressions inside the function in the function's scope.
-   The call step's `if` gates the whole function as a single unit.

## Nesting

A custom function can call other custom functions and built-in `eas/*` functions. Currently, custom functions cannot call `eas/build` or `eas/maestro_test`. EAS Workflows resolves every nested path relative to the EAS project directory, not the directory containing the calling function.

You can nest custom functions up to 10 levels deep. A custom function cannot call itself, either directly or through other custom functions.

## Example

**.eas/functions/greet/function.yml** defines a custom function with one input, one output, and one step:

```yaml
name: Greet
inputs:
  - name: who
    default_value: world
outputs:
  message:
    value: '${{ steps.make.outputs.message }}'
runs:
  steps:
    - id: make
      run: set-output message "Hello, ${{ inputs.who }}!"
```

A workflow calls it with `uses: ./.eas/functions/greet`, passes an input with `with:`, and reads the output from `${{ steps.greet.outputs.message }}`:

```yaml
name: Hello
jobs:
  greet:
    steps:
      - id: greet
        uses: ./.eas/functions/greet
        with:
          who: Expo
      - run: echo "${{ steps.greet.outputs.message }}"
```

You can also call a custom function from a [hook](/eas/workflows/syntax.md#jobsjob_idhooks):

```yaml
jobs:
  build_ios:
    type: build
    params:
      platform: ios
    hooks:
      before_install_node_modules:
        - uses: ./.eas/functions/setup
```