System Initiative

# Attribute Functions Attribute functions are a kind of [function](./function.md) used to set properties on [components](./components.md) using data from other properties on the same or other components. They are the primary mechanism for transforming data within a component. ## How Attribute Functions Work Attribute functions execute automatically whenever their input data changes. They take data from one or more sources (such as other component properties) and compute a result that is stored in a specific location within the component's property tree. Each attribute function has: - **Arguments**: The input data sources the function needs to perform its computation - **Bindings**: The configuration that specifies where the function's output will be stored and where each argument's data comes from - **Output location**: A path in the component's property tree where the function's return value is stored ## When Attribute Functions Run Attribute functions execute automatically in these scenarios: - When a component is first created - When a subscription receives new data - When a property that the function depends on changes - After other attribute functions that this function depends on complete System Initiative determines the correct execution order based on the dependencies between attribute functions. ## Attribute Function Arguments Attribute functions receive a single `input` object as their argument. The properties on this object are determined by the Arguments section in the function's metadata panel. Each argument has: - **Name**: Used as the property name on the `input` object - **Type**: One of Any, Array, Boolean, Integer, JSON, Map, Object, or String These types map directly to their TypeScript equivalents and align with schema property kinds. ## Attribute Function Bindings Bindings connect the function's arguments to their data sources and specify where the output goes. For each attribute function, you configure: - **Output location**: A path (like `/domain/snack`) where the function's return value will be stored - **Argument sources**: For each function argument, specify whether its data comes from a subscription or another property in the same component For example, an attribute function that writes to the `snack` attribute from the value of the `Yummy` property subscription would have: - A function argument named `yummy` with its source set to the `Yummy` property via a subscription - An output location of `/domain/snack` Bindings are configured in the `Bindings` sub-panel of the function's metadata. ## Common Use Cases Attribute functions are commonly used for: - **Data transformation**: Converting input data from one format to another - **Computed properties**: Calculating values based on other component properties - **API interactions**: Fetching data from external services to populate component properties - **Complex data manipulation**: Using lodash or custom logic to transform data structures ## See Also For detailed examples and technical implementation details, see the [Attribute Function Examples](/reference/function#attribute-function-examples) section in the Functions Reference.