Implementing the OnPush Change Detection Strategy in Angular

Angular's default change detection strategy can sometimes lead to unnecessary component updates, impacting performance. This challenge asks you to implement a component that utilizes the OnPush change detection strategy to optimize updates and only re-render when its inputs explicitly change. Understanding and applying OnPush is crucial for building performant Angular applications.

Problem Description

You are tasked with creating an Angular component called DataDisplayComponent that displays data received as input. This component must utilize the OnPush change detection strategy. The component should receive an array of numbers as input (data) and display each number in a list. The component should only re-render when the data input array changes its reference (e.g., a new array is assigned, not just when elements within the array are modified).

Key Requirements:

• OnPush Strategy: The component must be configured to use the OnPush change detection strategy.
• Input Binding: The component must accept an input property named data of type number[].
• Data Display: The component must display the numbers from the data array in an unordered list (<ul>).
• Change Detection Trigger: The component should not re-render when elements within the data array are modified. It should only re-render when a new array is assigned to the data input.

Expected Behavior:

1. Initially, the component should render the data provided in the data input.
2. If the data input is replaced with a new array (a new array object is assigned), the component should re-render to display the new data.
3. If the contents of the data array are modified (e.g., pushing a new number to the array), the component should not re-render.

Edge Cases to Consider:

• Empty input array: The component should render an empty list.
• Null or undefined input: The component should handle null or undefined input gracefully (e.g., display a message or render an empty list). For simplicity, assume the input will always be an array or null/undefined.

Examples

Example 1:

Input: data = [1, 2, 3]
Output: <ul><li>1</li><li>2</li><li>3</li></ul>
Explanation: The component renders the initial data.

Example 2:

Input: data = [1, 2, 3] (initial)
data = [4, 5, 6] (new array assigned)
Output: <ul><li>4</li><li>5</li><li>6</li></ul>
Explanation: The component re-renders because a new array was assigned to the data input.

Example 3:

Input: data = [1, 2, 3] (initial)
data.push(4)  // Modifying the existing array
Output: <ul><li>1</li><li>2</li><li>3</li></ul>
Explanation: The component does *not* re-render because the existing array was modified, not replaced.

Constraints

• The component must be a standard Angular component.
• The solution must be written in TypeScript.
• The component should be self-contained and not rely on external services or modules beyond standard Angular functionality.
• Performance is a key consideration; the OnPush strategy should be correctly implemented to avoid unnecessary re-renders.

Notes

• Remember to set the changeDetection property to OnPush in the component's @Component decorator.
• Think carefully about how Angular's change detection works and how OnPush affects it.
• Consider using a simple parent component to provide the data input and demonstrate the expected behavior. You don't need to build a full application, just a minimal example to showcase the DataDisplayComponent.
• Debugging can be tricky; use the Angular DevTools to inspect change detection cycles and verify that the component is only re-rendering when expected.