Set Up Modus Event Listeners

Set Up Modus Event Listeners

Properly set up and clean up event listeners for Modus web components following established patterns.

When to Use

Use this skill when:

• Adding event handling to any Modus wrapper component
• Components need to respond to web component events
• You need to sync React state with web component state
• Handling user interactions from Modus components

Pattern Overview

All Modus event listeners follow this pattern:

1. Use useRef to get component reference
2. Use useEffect to set up listeners
3. Check for component existence before adding listeners
4. Create typed handler functions for each event
5. Conditionally attach listeners based on prop existence
6. Return cleanup function to remove listeners

Reference Examples

• Simple events: src/components/ModusCheckbox.tsx:91-150
• Multiple events: src/components/ModusDropdownMenu.tsx:79-112
• Complex events: src/components/ModusNavbar.tsx (multiple event handlers)

Basic Template

import { useEffect, useRef } from "react";
import { ModusWcComponent } from "@trimble-oss/moduswebcomponents-react";

export default function ModusComponent({
  onEventName,
}: {
  onEventName?: (event: CustomEvent<EventDetailType>) => void;
}) {
  const componentRef = useRef<HTMLModusWcComponentElement>(null);

  useEffect(() => {
    const component = componentRef.current;
    if (!component) return;

    const handleEventName = (event: Event) => {
      onEventName?.(event as CustomEvent<EventDetailType>);
    };

    if (onEventName) {
      component.addEventListener("eventName", handleEventName);
    }

    return () => {
      if (onEventName) {
        component.removeEventListener("eventName", handleEventName);
      }
    };
  }, [onEventName]);

  return <ModusWcComponent ref={componentRef} />;
}

Multiple Event Handlers

export default function ModusComponent({
  onInputChange,
  onInputFocus,
  onInputBlur,
  onValueChange,
}: {
  onInputChange?: (event: CustomEvent<InputEvent>) => void;
  onInputFocus?: (event: CustomEvent<FocusEvent>) => void;
  onInputBlur?: (event: CustomEvent<FocusEvent>) => void;
  onValueChange?: (event: CustomEvent<boolean>) => void;
}) {
  const componentRef = useRef<HTMLModusWcComponentElement>(null);

  useEffect(() => {
    const component = componentRef.current;
    if (!component) return;

    const handleInputChange = (event: Event) => {
      onInputChange?.(event as CustomEvent<InputEvent>);
    };
    const handleInputFocus = (event: Event) => {
      onInputFocus?.(event as CustomEvent<FocusEvent>);
    };
    const handleInputBlur = (event: Event) => {
      onInputBlur?.(event as CustomEvent<FocusEvent>);
    };
    const handleValueChange = (event: Event) => {
      onValueChange?.(event as CustomEvent<boolean>);
    };

    if (onInputChange)
      component.addEventListener("inputChange", handleInputChange);
    if (onInputFocus)
      component.addEventListener("inputFocus", handleInputFocus);
    if (onInputBlur)
      component.addEventListener("inputBlur", handleInputBlur);
    if (onValueChange)
      component.addEventListener("inputChange", handleValueChange);

    return () => {
      if (onInputChange)
        component.removeEventListener("inputChange", handleInputChange);
      if (onInputFocus)
        component.removeEventListener("inputFocus", handleInputFocus);
      if (onInputBlur)
        component.removeEventListener("inputBlur", handleInputBlur);
      if (onValueChange)
        component.removeEventListener("inputChange", handleValueChange);
    };
  }, [onInputChange, onInputFocus, onInputBlur, onValueChange]);

  return <ModusWcComponent ref={componentRef} />;
}

Key Patterns

1. Null Check First

Always check if component exists:

useEffect(() => {
  const component = componentRef.current;
  if (!component) return; // ✅ Early return if no component
  
  // Set up listeners
}, [dependencies]);

2. Conditional Listener Attachment

Only attach listeners if handlers are provided:

if (onEventName) {
  component.addEventListener("eventName", handleEventName);
}

3. Proper Cleanup

Always remove listeners in cleanup:

return () => {
  if (onEventName) {
    component.removeEventListener("eventName", handleEventName);
  }
};

4. Type Casting

Cast events to proper CustomEvent types:

const handleEvent = (event: Event) => {
  onEvent?.(event as CustomEvent<EventDetailType>);
};

5. Dependencies Array

Include all handler props in dependencies:

useEffect(() => {
  // ...
}, [onEventName, onOtherEvent]); // ✅ Include all handlers

Common Event Names

Modus components use these event names:

Check Modus documentation for component-specific events.

Advanced Patterns

Event with Side Effects

const handleItemSelect = (event: Event) => {
  const customEvent = event as CustomEvent<{ value: string }>;
  onItemSelect?.(customEvent);

  // Close menu after selection
  const dropdown = dropdownRef.current;
  if (dropdown) {
    dropdown.menuVisible = false;
  }
};

Reference: src/components/ModusDropdownMenu.tsx:86-94

Event Value Transformation

const handleValueChange = (event: Event) => {
  const customEvent = event as CustomEvent<InputEvent>;
  
  // Transform or validate value
  const rawValue = (customEvent.target as HTMLModusWcComponentElement).value;
  const transformedValue = transformValue(rawValue);
  
  onValueChange?.(new CustomEvent("valueChange", {
    detail: transformedValue,
  }));
};

Debounced Events

import { useCallback } from "react";
import { debounce } from "lodash"; // or your debounce utility

useEffect(() => {
  const component = componentRef.current;
  if (!component) return;

  const debouncedHandler = debounce((event: Event) => {
    onSearchChange?.(event as CustomEvent<{ value: string }>);
  }, 300);

  component.addEventListener("searchChange", debouncedHandler);

  return () => {
    component.removeEventListener("searchChange", debouncedHandler);
    debouncedHandler.cancel(); // Cancel pending debounced calls
  };
}, [onSearchChange]);

Common Mistakes

1. Missing cleanup: Always return cleanup function
2. Wrong dependencies: Include all handler props in dependency array
3. Missing null check: Always check componentRef.current exists
4. Wrong event names: Check Modus docs for exact event names
5. Not removing listeners: Must remove in cleanup to prevent memory leaks
6. Type casting errors: Use proper CustomEvent types

Testing Checklist

• Event listeners are attached when component mounts
• Event listeners are removed when component unmounts
• Handlers are called when events fire
• Multiple handlers work correctly
• Cleanup prevents memory leaks
• TypeScript types are correct

Related Files

• src/components/ModusCheckbox.tsx - Basic event handling
• src/components/ModusDropdownMenu.tsx - Multiple events
• src/components/ModusNavbar.tsx - Complex event handling
• .cursor/rules/modus-react-integration.mdc - Integration patterns

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