1. Key Difference 1: Purpose and Scope: Chart.js is a simple and flexible charting library that focuses on creating responsive and visually appealing charts for web applications. It provides a wide range of chart types and customization options. On the other hand, D3.js (Data-Driven Documents) is a powerful JavaScript library that allows users to manipulate documents based on data. It provides a comprehensive set of data visualization tools and enables the creation of highly interactive and complex visualizations.

2. Key Difference 2: Approach: Chart.js follows a declarative approach, where charts can be easily created using predefined configurations and options. It provides a simple API for configuring various properties of a chart, making it beginner-friendly. In contrast, D3.js follows an imperative approach, where developers have full control over manipulating the DOM and data. It requires more coding and understanding of JavaScript and SVG (Scalable Vector Graphics) to create visualizations.

3. Key Difference 3: Learning Curve: Chart.js has a lower learning curve compared to D3.js. It provides a user-friendly and intuitive interface, making it easy for beginners to create basic charts without much coding knowledge. D3.js, on the other hand, has a steeper learning curve and requires a solid understanding of JavaScript and SVG concepts. It is more suitable for experienced developers who need extensive customization and complex data visualizations.

4. Key Difference 4: Chart Complexity: Chart.js is best suited for creating simple to moderately complex charts. It provides a wide range of built-in chart types like line, bar, pie, etc., along with customizable options for styling and animations. D3.js, on the other hand, is capable of creating highly intricate and custom visualizations. It allows users to create complex layouts, apply advanced data transformations, and handle large datasets efficiently.

5. Key Difference 5: Community Support and Resources: Chart.js has a large and active community, with extensive documentation, tutorials, and examples available. It has a well-maintained GitHub repository and frequent updates, ensuring ongoing support and bug fixes. D3.js also has a dedicated community, but it is relatively smaller compared to Chart.js. However, D3.js offers more flexibility due to its broader functionality, and users can find a range of examples and tutorials for specific needs.

6. Key Difference 6: Integration with Other Libraries: Chart.js is designed to be lightweight and can be easily integrated into existing web applications. It has fewer dependencies and can work well with other JavaScript frameworks like React or Angular. D3.js, on the other hand, is a standalone library that provides comprehensive data manipulation and visualization capabilities. It is often used as a foundation for building custom data visualization applications and is less focused on integration with other libraries.

In Summary, Chart.js is a user-friendly and flexible charting library, suitable for creating visually appealing charts with moderate complexity, while D3.js is a powerful data visualization library that allows extensive customization and intricate visualizations, but with a steeper learning curve and more demanding coding requirements.