feat(blog): retrospectively write beta 21 blog post

Blog post for beta 21 release

content/blog/2024/08/08/aurelia-2-beta-21.md

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+title = "What's New in Aurelia 2 Beta 21?"
+author = "Dwayne Charrington"
+description = "The Aurelia 2 Beta 21 release focuses on enhancing developer experience and addressing community-reported issues. Key improvements include support for increment/decrement assignment operators, fixes for the state plugin, router enhancements, and task queue refinements."
+date = 2024-08-08T12:00:00Z
+lastmod = 2024-08-08T12:00:00Z
+tags = ["aurelia2", "release"]
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+
+We're excited to announce the release of **Aurelia 2 Beta 21**! This release brings several highly requested features and important bug fixes to improve your development experience. Let's dive into what's new! 🚀
+
+## ✨ New Features
+
+### **Increment/Decrement Assignment Operators**
+
+One of our most requested features is finally here! Beta 21 introduces support for unary increment/decrement and assignment operators (`++`, `--`, `+=`, `-=`, `/=`, `*=`). This allows for more concise and expressive code in your templates.
+
+**Example:**
+```html
+<button @click="value++">Increment</button>
+<button @click="value += 2">Increment by 2</button>
+```
+
+> **Important Note:** Using these operators in non-trigger bindings will result in an error (`AUR0113`) to prevent infinite update-eval loops.
+
+```html
+<!-- ❌ These will throw AUR0113 -->
+<div>${value++}</div>
+<my-component :prop="value++"></my-component>
+```
+
+## 🐞 Bug Fixes
+
+### **State Plugin Improvements**
+The state plugin received a critical fix ensuring all queued actions are properly executed. Previously, the last action in a queue might not be called if an action handler returned a promise that resolved after the second action was dispatched. ([#2023](https://github.com/aurelia/aurelia/pull/2023))
+
+### **Router Enhancements**
+- **Router-Lite**: Fixed element injection for routed view-models ([#2012](https://github.com/aurelia/aurelia/pull/2012))
+- **Default Child Routes**: Resolved issues with filtering available endpoints ([#2013](https://github.com/aurelia/aurelia/pull/2013))
+- **History Strategy**: Fixed router-lite behavior when `historyStrategy` is set to `none` ([#2005](https://github.com/aurelia/aurelia/pull/2005))
+
+### **Task Queue Refinements**
+- Fixed timing issues with multiple persistent delayed tasks ([#2007](https://github.com/aurelia/aurelia/pull/2007))
+- Improved task queue processing loop for better reliability
+
+### **Development Experience**
+- **Vite Plugin**: Resolved vitest issues on Windows with HTML files ([#2006](https://github.com/aurelia/aurelia/pull/2006))
+- **Types**: Improved bindable definitions for better TypeScript support ([#2010](https://github.com/aurelia/aurelia/pull/2010))
+
+## 🔄 Refactorings
+
+- **Task Queue**: Removed the 'reusable' parameter for simpler implementation ([#2008](https://github.com/aurelia/aurelia/pull/2008))
+- **Binding**: Enhanced handling of binding glitches ([#2020](https://github.com/aurelia/aurelia/pull/2020))
+
+## 📥 How to Upgrade
+
+To upgrade to Aurelia 2 Beta 21:
+1. Update your project dependencies to the latest version
+2. Test your application thoroughly, particularly if you're using the state plugin or router features
+3. Take advantage of the new increment/decrement operators in your templates!
+
+## 🔗 Additional Resources
+
+For a complete list of changes, check out the [full changelog](https://github.com/aurelia/aurelia/compare/v2.0.0-beta.20...v2.0.0-beta.21).
+
+---
+
+We're continuously working to make Aurelia 2 better with each release. Thank you to all our contributors and community members for your ongoing support and feedback! 💪