When should I use Inline vs. External JavaScript?

Trade-off Analysis

Performant Pages vs. Load Times

While inline JavaScript offers convenience for minor tasks, it could lead to higher initial page load times as it's parsed side-by-side with HTML. Conversely, external JavaScript can be deferred or loaded asynchronously, reducing initial load times.

Scalability and Maintenance

Inline scripts may get unwieldy in size as your project expands, making external scripts the best choice for long-term code maintainability and scalability.

Browser Caching Prowess

Inline scripts miss browser caching perks. By contrast, external scripts loaded once are cached, minimizing future HTTP requests and therefore, quicker page loads.

Instances favoring Inline/External scripts

• Configuration Initialization: Use inline scripts to initialize configuration parameters unique to a single page.
• Tiny Event Handlers: Inline adequately handles very simple events such as show/hide actions or basic element styling.
• Library/Framework Loading: Large libraries like jQuery or frameworks like React.js should be loaded externally to utilize browsers' caching function and for better code organization.
• Variable Script Loading: Conditional script loading based on certain user inputs/actions benefits from external script's flexibility.

Best Practices and Considerations

Inline Script Guidelines

• Minimalistic Approach: Make Inline JavaScript the right-hand tool for small business - pun intended.
• Code Clones - The Duplicates: If the same inline code is found multiple times, it’s time to externalize!

External Script Guidelines

• Modular to the Core: Modularize and compartmentalize code into different files for an organized codebase.
• The Modern Way: Bundle and reduce scripts' size with modern tools like webpack for fast loading.
• Async and Defer: async and defer in script tags control loading sequence steering clear from DOM blocking.

Accessibility

• Enhance, Not Replace: JavaScript should enhance HTML functionality, not replace it. This caters to all users, irrespective of their browser’s JavaScript capabilities.
• User Experience: User experience trumps everything! Ensure scripts do not impact the core user experience.

Inline vs. External: Real-life Applications

Inline JavaScript - A by-gone Era?

Inline scripting has been reduced largely to small tasks or quick prototyping. With HTTP/2's efficient multiple file loading, inline scripts' utility is dwindling even further, foregrounding the external file approach.

External JavaScript - The Future's Favourite

The growing trend of Single-Page Applications (SPAs) and complex web architectures necessitates external JavaScript use. With cleaner codebases and optimized load times via minification and bundling, external scripts foster a scalable and maintainable project structure.