Modal pattern with intercepting routes in NextJS - Step-by-Step Execution

Concept Flow - Modal pattern with intercepting routes

User clicks link

↓

Intercept route change

↓

Show modal overlay

↓

Render modal content

↓

User closes modal

↓

Restore previous page route

When a user clicks a link, the app intercepts the route change to show a modal overlay instead of a full page. Closing the modal restores the previous route.

Execution Sample

NextJS

import { useRouter } from 'next/navigation';
import { useState } from 'react';

export default function Page() {
  const router = useRouter();
  const [modalOpen, setModalOpen] = useState(false);

  function openModal() {
    setModalOpen(true);
    router.push('/modal-route');
  }

  function closeModal() {
    setModalOpen(false);
    router.back();
  }

  return (
    <>
      <button onClick={openModal}>Open Modal</button>
      {modalOpen && (
        <div role="dialog" aria-modal="true">
          <p>Modal Content</p>
          <button onClick={closeModal}>Close</button>
        </div>
      )}
    </>
  );
}

This code shows a button that opens a modal by intercepting route change and renders modal content. Closing the modal goes back to the previous route.

Execution Table

Step	User Action	State modalOpen	Router Action	Rendered Output
1	Page loads	false	Current route '/'	Button 'Open Modal' visible
2	User clicks 'Open Modal'	true	router.push('/modal-route')	Modal overlay with content shown
3	User clicks 'Close' in modal	false	router.back() to '/'	Modal closes, back to main page
4	User tries to navigate normally	false	Normal route change	Page changes normally, no modal

💡 Modal closes and route returns to previous page, normal navigation resumes.

Variable Tracker

Variable	Start	After Step 2	After Step 3	Final
modalOpen	false	true	false	false
router route	'/'	'/modal-route'	'/'	depends on user navigation

Key Moments - 3 Insights

Why does the modalOpen state change before the router.push?

Because setting modalOpen to true triggers React to render the modal overlay immediately, then router.push updates the URL. See execution_table step 2.

What happens if the user closes the modal but router.back() fails?

The modalOpen state is set to false, so the modal closes visually, but the URL might not change. This can cause mismatch. Always ensure router.back() works or handle fallback.

Why do we intercept route changes instead of normal navigation?

Intercepting lets us show modal content on top without full page reload, improving user experience. See concept_flow for the logical steps.

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of modalOpen after the user clicks 'Open Modal'?

A undefined

B true

C false

D null

💡 Hint

Check execution_table row 2 under 'State modalOpen'

At which step does the router navigate back to the previous page?

A Step 3

B Step 2

C Step 1

D Step 4

💡 Hint

Look at execution_table row 3 under 'Router Action'

If modalOpen was never set to true, what would happen when clicking 'Open Modal'?

A Modal would open but URL stays the same

B Both modal and URL change correctly

C Modal would not open but URL changes

D Nothing happens

💡 Hint

Refer to variable_tracker for modalOpen state changes and router actions

Concept Snapshot

Modal pattern with intercepting routes in Next.js:
- Intercept route changes to show modal overlay
- Use state (e.g., modalOpen) to control modal visibility
- Push new route for modal content
- Close modal by setting state false and router.back()
- Improves UX by avoiding full page reloads

Full Transcript

This visual execution shows how the modal pattern with intercepting routes works in Next.js. When the user clicks the 'Open Modal' button, the app sets modalOpen state to true and pushes a new route to show modal content. The modal appears as an overlay with accessible dialog roles. Closing the modal sets modalOpen to false and navigates back to the previous route. The execution table tracks each step, showing state changes and router actions. Key moments clarify why state changes happen before routing and why intercepting routes improves user experience. The visual quiz tests understanding of modalOpen state and router navigation steps.