Main class for server-side Interactivity API processing.

Source: wp-includes/interactivity-api/class-wp-interactivity-api.php
Since: 6.5.0

final class WP_Interactivity_API

Properties

$directive_processors

private static array $directive_processors

Maps directive attribute names to their processor methods.

Value:

array(
    'data-wp-interactive'   => 'data_wp_interactive_processor',
    'data-wp-router-region' => 'data_wp_router_region_processor',
    'data-wp-context'       => 'data_wp_context_processor',
    'data-wp-bind'          => 'data_wp_bind_processor',
    'data-wp-class'         => 'data_wp_class_processor',
    'data-wp-style'         => 'data_wp_style_processor',
    'data-wp-text'          => 'data_wp_text_processor',
    'data-wp-each'          => 'data_wp_each_processor',
)

$state_data

private array $state_data = array()

Initial state for each store namespace. Serialized and sent to client for hydration.

$config_data

private array $config_data = array()

Configuration for each store namespace. Accessible client-side via getConfig().

$derived_state_closures

private array $derived_state_closures = array()

Since: 6.9.0. Tracks derived state closures accessed during SSR for lazy client hydration.

$has_processed_router_region

private bool $has_processed_router_region = false

Whether data-wp-router-region has been processed (triggers loading bar styles).

$script_modules_that_can_load_on_client_navigation

private array $script_modules_that_can_load_on_client_navigation = array()

Since: 6.9.0. Script modules compatible with client-side navigation.

$namespace_stack

private ?array $namespace_stack = null

Since: 6.6.0. Stack of namespaces from data-wp-interactive during processing.

$context_stack

private ?array $context_stack = null

Since: 6.6.0. Stack of contexts from data-wp-context during processing.

$current_element

private ?array $current_element = null

Since: 6.7.0. Array representation of element currently being processed.

Public Methods

state()

Gets and/or sets initial state for a store namespace.

public function state( ?string $store_namespace = null, ?array $state = null ): array

Since: 6.5.0
Since: 6.6.0 — $store_namespace is optional during directive processing.

Parameters:

Returns: array — Current state for namespace.

Behavior:

• If $store_namespace is null/empty and $state is provided → _doing_it_wrong
• If $store_namespace is omitted during processing → uses current namespace from stack
• Merges $state recursively with existing state via array_replace_recursive()

config()

Gets and/or sets configuration for a store namespace.

public function config( string $store_namespace, array $config = array() ): array

Since: 6.5.0

Parameters:

Returns: array — Current config for namespace.

get_context()

Returns context for a namespace from the context stack.

public function get_context( ?string $store_namespace = null ): array

Since: 6.6.0

Parameters:

Returns: array — Context for namespace, or empty array.

Note: Only valid during process_directives(). Triggers _doing_it_wrong otherwise.

get_element()

Returns array representation of current element being processed.

public function get_element(): ?array

Since: 6.7.0

Returns: array{attributes: array<string, string|bool>}|null

Note: Only valid during process_directives().

add_hooks()

Registers necessary hooks for the Interactivity API.

public function add_hooks(): void

Since: 6.5.0
Since: 6.9.0 — Adds client-side navigation support.

Hooks Added:

• script_module_data_@wordpress/interactivity → filter_script_module_interactivity_data()
• script_module_data_@wordpress/interactivity-router → filter_script_module_interactivity_router_data()
• wp_script_attributes → add_load_on_client_navigation_attribute_to_script_modules()

filter_script_module_interactivity_data()

Filters script module data for @wordpress/interactivity.

public function filter_script_module_interactivity_data( array $data ): array

Since: 6.7.0
Since: 6.9.0 — Serializes derived state props.

Parameters:

Returns: array — Data with state, config, and derivedStateClosures added.

filter_script_module_interactivity_router_data()

Filters script module data for @wordpress/interactivity-router.

public function filter_script_module_interactivity_router_data( array $data ): array

Since: 6.7.0

Returns: array — Data with i18n strings for loading/loaded messages.

add_load_on_client_navigation_attribute_to_script_modules()

Adds data-wp-router-options attribute to compatible script modules.

public function add_load_on_client_navigation_attribute_to_script_modules( $attributes ): array

Since: 6.9.0

Parameters:

Returns: array — Modified attributes with data-wp-router-options JSON.

add_client_navigation_support_to_script_module()

Marks a script module as compatible with client-side navigation.

public function add_client_navigation_support_to_script_module( string $script_module_id ): void

Since: 6.9.0

Parameters:

process_directives()

Processes interactivity directives in HTML content.

public function process_directives( string $html ): string

Since: 6.5.0

Parameters:

Returns: string — Processed HTML, or original if unbalanced tags.

Behavior:

1. Early return if no data-wp- found
2. Initializes namespace and context stacks
3. Calls _process_directives() for actual work
4. Cleans up stacks
5. Returns original HTML if processing returned null (unbalanced)

print_router_markup()

Outputs loading bar markup for the interactivity router.

public function print_router_markup(): void

Since: 6.7.0

Output:

<div
    class="wp-interactivity-router-loading-bar"
    data-wp-interactive="core/router"
    data-wp-class--start-animation="state.navigation.hasStarted"
    data-wp-class--finish-animation="state.navigation.hasFinished"
></div>

Deprecated Methods

print_client_interactivity_data()

public function print_client_interactivity_data(): void

Deprecated: 6.7.0. Use script_module_data_{$module_id} filter instead.

register_script_modules()

public function register_script_modules(): void

Deprecated: 6.7.0. Use wp_default_script_modules() instead.

print_router_loading_and_screen_reader_markup()

public function print_router_loading_and_screen_reader_markup(): void

Deprecated: 6.7.0. Use print_router_markup() instead.

Private Methods

_process_directives()

Internal processing of directives using shared stacks.

private function _process_directives( string $html ): ?string

Since: 6.6.0

Returns: string|null — Processed HTML or null if unbalanced.

Processing Order:

1. Create WP_Interactivity_API_Directives_Processor
2. Skip SVG and MATH tags (incompatible with Tag Processor)
3. Track balanced tags via stack
4. For each tag with directives, run processors in order
5. On exit, run processors in reverse order
6. Return null if unbalanced tags detected

evaluate()

Evaluates a directive reference path against state/context.

private function evaluate( array $entry ): mixed

Since: 6.5.0
Since: 6.6.0 — Supports derived state.
Since: 6.9.0 — Receives $entry array instead of string.

Parameters:

Returns: mixed|null — Evaluated value, negated if prefixed with !.

Special Cases:

• !path → Returns negated value
• .length on arrays/strings → Returns count/strlen (since 6.8.0)
• Closures → Executed with namespace pushed to stack, tracked for hydration

parse_directive_name()

Parses directive attribute name into components.

private function parse_directive_name( string $directive_name ): ?array

Since: 6.9.0

Returns:

array(
    'prefix'    => string,  // Main directive name without "data-wp-"
    'suffix'    => ?string, // After first "--"
    'unique_id' => ?string, // After "---"
)

Examples:

• data-wp-bind--src → ['prefix' => 'bind', 'suffix' => 'src', 'unique_id' => null]
• data-wp-class--active---123 → ['prefix' => 'class', 'suffix' => 'active', 'unique_id' => '123']

extract_directive_value()

Extracts namespace and value from directive attribute.

private function extract_directive_value( $directive_value, $default_namespace = null ): array

Since: 6.5.0

Returns: array — [namespace, value]

Examples:

• 'state.foo' → ['defaultNs', 'state.foo']
• 'otherPlugin::state.foo' → ['otherPlugin', 'state.foo']
• '{"isOpen": false}' → ['defaultNs', ['isOpen' => false]]

get_directive_entries()

Gets all valid directive entries for a prefix from current element.

private function get_directive_entries( WP_Interactivity_API_Directives_Processor $p, string $prefix ): array

Since: 6.9.0

Returns: array — Sorted array of entries with namespace, value, suffix, unique_id.

kebab_to_camel_case()

Converts kebab-case to camelCase.

private function kebab_to_camel_case( string $str ): string

Since: 6.5.0

Example: 'my-variable-name' → 'myVariableName'

merge_style_property()

Merges a style property into a style attribute string.

private function merge_style_property( string $style_attribute_value, string $style_property_name, $style_property_value ): string

Since: 6.5.0

Examples:

• merge_style_property('color:green;', 'color', 'red') → 'color:red;'
• merge_style_property('background:green;', 'color', 'red') → 'background:green;color:red;'
• merge_style_property('color:green;', 'color', null) → ''

get_router_animation_styles()

Returns CSS for the router loading bar animation.

private function get_router_animation_styles(): string

Since: 6.5.0

Directive Processors

All processors receive:

• WP_Interactivity_API_Directives_Processor $p — The processor instance
• string $mode — 'enter' or 'exit'
• array &$tag_stack — Reference to tag stack (only data_wp_each_processor)

data_wp_interactive_processor()

Processes data-wp-interactive directive.

private function data_wp_interactive_processor( WP_Interactivity_API_Directives_Processor $p, string $mode ): void

Since: 6.5.0

Behavior:

• enter: Parses namespace from attribute value (string or JSON {"namespace":"..."}) and pushes to stack
• exit: Pops namespace from stack

data_wp_context_processor()

Processes data-wp-context directive.

private function data_wp_context_processor( WP_Interactivity_API_Directives_Processor $p, string $mode ): void

Since: 6.5.0

Behavior:

• enter: Merges context JSON into stack with namespace key
• exit: Pops context from stack

data_wp_bind_processor()

Processes data-wp-bind--{attr} directives.

private function data_wp_bind_processor( WP_Interactivity_API_Directives_Processor $p, string $mode ): void

Since: 6.5.0

Behavior:

• Evaluates reference and sets/removes attribute
• Boolean values for aria-* and data-* become "true"/"false" strings
• false removes non-aria/data attributes

data_wp_class_processor()

Processes data-wp-class--{classname} directives.

private function data_wp_class_processor( WP_Interactivity_API_Directives_Processor $p, string $mode ): void

Since: 6.5.0

Behavior:

• Truthy value adds class
• Falsy value removes class
• Supports unique IDs: data-wp-class--active---123 → class active---123

data_wp_style_processor()

Processes data-wp-style--{property} directives.

private function data_wp_style_processor( WP_Interactivity_API_Directives_Processor $p, string $mode ): void

Since: 6.5.0

Behavior:

• Updates or removes style property in style attribute
• Removes entire style attribute if empty after modification

data_wp_text_processor()

Processes data-wp-text directive.

private function data_wp_text_processor( WP_Interactivity_API_Directives_Processor $p, string $mode ): void

Since: 6.5.0

Behavior:

• Replaces element content with evaluated value (escaped)
• Only processes strings and numbers (per Preact behavior)
• Other types clear the content

data_wp_router_region_processor()

Processes data-wp-router-region directive.

private function data_wp_router_region_processor( WP_Interactivity_API_Directives_Processor $p, string $mode ): void

Since: 6.5.0

Behavior:

• Only runs once per page
• Registers and enqueues wp-interactivity-router-animations styles
• Adds print_router_markup() to wp_footer

data_wp_each_processor()

Processes data-wp-each directive on <template> tags.

private function data_wp_each_processor( WP_Interactivity_API_Directives_Processor $p, string $mode, array &$tag_stack ): void

Since: 6.5.0
Since: 6.9.0 — Includes list path in data-wp-each-child.

Behavior:

1. Only processes <template> tags
2. Evaluates array reference
3. Skips if: manual SSR (data-wp-each-child exists), non-list array, or invalid template content
4. For each item:
   • Creates context with item (name from suffix, default item)
   • Recursively processes inner content
   • Adds data-wp-each-child to top-level rendered elements
5. Appends all processed content after template closer

Example:

<template data-wp-each="state.items" data-wp-each-key="context.item.id">
    <li data-wp-text="context.item.name"></li>
</template>