Implementing Vue's nextTick in TypeScript

Vue's reactivity system updates the DOM asynchronously. This means that after you change reactive data, the DOM might not reflect that change immediately. The nextTick function is crucial for ensuring that your code runs after the DOM has been updated, allowing you to reliably interact with the updated DOM. This challenge asks you to implement a simplified version of nextTick in TypeScript.

Problem Description

You need to create a function named nextTick that accepts a callback function. This nextTick function should ensure that the provided callback is executed after the current JavaScript execution queue is flushed and the DOM has been updated.

Key Requirements:

1. Asynchronous Execution: The callback must be executed asynchronously, not synchronously.
2. DOM Update Guarantee (Simulated): For the purpose of this challenge, we will simulate DOM updates. You should assume that any pending DOM updates will have occurred by the time your callback executes.
3. Queueing Multiple Callbacks: If nextTick is called multiple times before the pending callbacks are executed, all callbacks should be queued and executed in the order they were registered.
4. TypeScript Implementation: The solution must be written in TypeScript.

Expected Behavior:

When nextTick(callback) is called, the callback function should be scheduled to run. If multiple calls to nextTick occur, they should be batched and executed in order.

Edge Cases:

• Calling nextTick multiple times in rapid succession.
• Callbacks that themselves might schedule further nextTick calls.

Examples

Example 1:

// Assume this is the environment where nextTick is defined

let message = 'Initial';

function updateDOM() {
  // In a real Vue app, this would trigger DOM updates
  console.log('DOM updated with:', message);
}

nextTick(() => {
  console.log('Callback 1 executed. Message:', message); // Expected: Callback 1 executed. Message: Updated
  updateDOM();
});

message = 'Updated';

console.log('After message update, before nextTick callback');
// Expected output:
// After message update, before nextTick callback
// Callback 1 executed. Message: Updated
// DOM updated with: Updated

Example 2:

// Assume this is the environment where nextTick is defined

let counter = 0;

function logCounter(id: number) {
  console.log(`Callback ${id} executed. Counter: ${counter}`);
}

nextTick(() => logCounter(1));
nextTick(() => logCounter(2));

counter = 10;

// Expected output (order of callbacks is guaranteed):
// Callback 1 executed. Counter: 10
// Callback 2 executed. Counter: 10

Example 3: Nested nextTick

// Assume this is the environment where nextTick is defined

let value = 'A';

console.log('Before initial nextTick');

nextTick(() => {
  console.log('Outer callback executed. Value:', value); // Expected: Outer callback executed. Value: B

  nextTick(() => {
    console.log('Inner callback executed. Value:', value); // Expected: Inner callback executed. Value: C
  });

  value = 'B'; // This change should be seen by the inner callback
});

value = 'C'; // This change should be seen by the outer callback

console.log('After initial nextTick setup');

// Expected output:
// Before initial nextTick
// After initial nextTick setup
// Outer callback executed. Value: C
// Inner callback executed. Value: B

Constraints

• The nextTick function should be a standalone function, not part of a class.
• The implementation should be efficient for queuing a large number of callbacks.
• You should not rely on any external libraries or framework-specific APIs (other than standard JavaScript/TypeScript features and browser/Node.js event loop mechanisms).

Notes

Consider how the browser/Node.js event loop handles microtasks and macrotasks. setTimeout(callback, 0) is a common way to defer execution to the next macrotask. For a more sophisticated implementation that prioritizes microtasks (like Promise.resolve().then(callback)), you might consider using promises. Think about how to collect all callbacks to be run in a single flush.