1. Project Overview
Cat.js is a lightweight, state-of-the-art engine designed to build powerful User Interfaces (UIs). It prioritizes the highest performance and efficiency, based exclusively on modern native browser APIs, primarily Web Components.

- Version: 0.1.0 (as of October 1, 2024)

2. Core Concepts and Principles
- Utilizes modern native browser APIs, especially Web Components
- Focuses on maximum performance and efficiency
- Promotes a lightweight approach to UI development
- Emphasizes simplicity and ease of use

3. Technical Details

Key Features
- Client-Side Compiler (CSC) before loading the DOM
- Attachment through a script:src tag in the head of HTML documents
- Written in vanilla, low-level JavaScript optimized for browser runtime
- Beautiful and easy-to-use syntax
- Efficient project tree structure
- Compiles everything on the loading stage.
- Everything that was compiled it's "0-dependency", neither of cat.js.

Implementation Details
- No Virtual DOM or similar abstractions
- Avoids use of bundlers, Webpack, polyfills, etc.
- Discourages writing HTML or CSS code within JavaScript files
- Eliminates render methods for components and logic that trigger unnecessary reflows and repainting
- Avoid treat Cat.js as a runtime at any cost.

4. Code

```

// Cat.js

// Immediately Invoked Function Expression (IIFE) to encapsulate the compiler
(function() {
  'use strict';

  /**
   * Internal module for tracking loaded files.
   */
  const Registry = (function() {
    const loadedFiles = new Set();

    return {
      isFileLoaded: (path) => loadedFiles.has(path),
      markFileAsLoaded: (path) => loadedFiles.add(path),
    };
  })();

  /**
   * Compiler module for generating self-contained component classes.
   */
  const Compiler = (function() {
    /**
     * Compiles the component's template and script into a component class definition.
     * @param {string} name - The name of the component (e.g., 'my-component').
     * @param {string} templateContent - The inner HTML of the component's <template>.
     * @param {string} scriptContent - The content of the component's <script>.
     */
    function compileComponent(name, templateContent, scriptContent) {
      // Create a template element and pre-clone its content
      const templateElement = document.createElement('template');
      templateElement.innerHTML = templateContent;
      const templateContentClone = templateElement.content;

      // Process the template to find bindings
      const bindings = []; // Array to hold binding info
      const propertyNames = new Set();

      // Process nodes recursively
      const processNode = (node, path) => {
        if (node.nodeType === Node.TEXT_NODE) {
          const text = node.textContent;
          const parts = text.split(/(\{(?:[^}]+)\})/);
          let hasBinding = false;

          // Collect variable names inside { }
          for (let i = 0; i < parts.length; i++) {
            const part = parts[i];
            const match = part.match(/^\{([^}]+)\}$/);
            if (match) {
              const varName = match[1].trim();
              propertyNames.add(varName);
              hasBinding = true;
            }
          }

          if (hasBinding) {
            bindings.push({
              type: 'text',
              nodePath: path.slice(),
              varNames: getVariableNamesFromParts(parts),
              parts: parts,
            });
          }
        } else if (node.nodeType === Node.ELEMENT_NODE) {
          if (node.nodeName.toLowerCase() === 'style') {
            // Do not process the content of style tags
            return;
          }

          // Process attributes
          for (let attr of Array.from(node.attributes)) {
            const value = attr.value;
            const parts = value.split(/(\{(?:[^}]+)\})/);
            let hasBinding = false;

            // Collect variable names inside { }
            for (let i = 0; i < parts.length; i++) {
              const part = parts[i];
              const match = part.match(/^\{([^}]+)\}$/);
              if (match) {
                const varName = match[1].trim();
                propertyNames.add(varName);
                hasBinding = true;
              }
            }

            if (hasBinding) {
              bindings.push({
                type: 'attribute',
                nodePath: path.slice(),
                attributeName: attr.name,
                varNames: getVariableNamesFromParts(parts),
                parts: parts,
              });
            }
          }

          // Process child nodes recursively
          node.childNodes.forEach((childNode, index) => {
            path.push(index);
            processNode(childNode, path);
            path.pop();
          });
        }
      };

      // Helper function to extract variable names from parts
      const getVariableNamesFromParts = (parts) => {
        const varNames = [];
        for (let i = 0; i < parts.length; i++) {
          const part = parts[i];
          const match = part.match(/^\{([^}]+)\}$/);
          if (match) {
            varNames.push(match[1].trim());
          }
        }
        return varNames;
      };

      // Start processing from templateElement.content
      templateElement.content.childNodes.forEach((node, index) => {
        processNode(node, [index]);
      });

      // Precompute propertyNames
      const properties = Array.from(propertyNames);

      // Generate the ComponentClass
      class ComponentClass extends HTMLElement {
        constructor() {
          super();
          const shadowRoot = this.attachShadow({ mode: 'open' });

          // Clone the template content into the shadowRoot
          shadowRoot.appendChild(ComponentClass.templateContent.cloneNode(true));

          // Initialize properties
          this._initProperties();

          // Setup bindings
          this._setupBindings(shadowRoot);
    
          // Initialize event listeners array
          this._eventListeners = [];
    
          // Execute user script in the context of 'this' safely
          if (ComponentClass.scriptFunction) {
            try {
              ComponentClass.scriptFunction.call(this);
            } catch (error) {
              console.error(`Error executing script in component ${name}: ${error.message}`);
            }
          }
        }

        _initProperties() {
          if (!this._propertyValues) {
            this._propertyValues = {};
          }
          // Initialize property values
          ComponentClass.properties.forEach(varName => {
            this._propertyValues[varName] = '';
          });
        }

        _setupBindings(shadowRoot) {
          this._bindingsMap = {};
          this._bindings = [];

          // Setup per-instance bindings
          ComponentClass.bindings.forEach(binding => {
            const node = this._getNodeByPath(shadowRoot, binding.nodePath);

            // Create a copy of the binding for this instance
            const instanceBinding = Object.assign({}, binding);
            instanceBinding.node = node;

            // For each varName in the binding, add the binding to _bindingsMap
            binding.varNames.forEach(varName => {
              if (!this._bindingsMap[varName]) {
                this._bindingsMap[varName] = [];
              }
              this._bindingsMap[varName].push(instanceBinding);
            });

            this._bindings.push(instanceBinding);
          });
        }

        _getNodeByPath(root, path) {
          let current = root;
          for (let i = 0; i < path.length; i++) {
            current = current.childNodes[path[i]];
          }
          return current;
        }

        _updateProperty(varName) {
          const bindings = this._bindingsMap[varName];
          if (bindings) {
            bindings.forEach(binding => {
              if (binding.type === 'text') {
                const newText = this._computeBindingText(binding);
                binding.node.textContent = newText;
              } else if (binding.type === 'attribute') {
                const newValue = this._computeBindingText(binding);
                binding.node.setAttribute(binding.attributeName, newValue);
              }
            });
          }
        }

        _computeBindingText(binding) {
          const computedParts = binding.parts.map(part => {
            const match = part.match(/^\{([^}]+)\}$/);
            if (match) {
              const varName = match[1].trim();
              return this[varName];
            } else {
              return part;
            }
          });
          return computedParts.join('');
        }

        connectedCallback() {
          // Any additional initialization can be done here
          if (typeof this.onConnected === 'function') {
            this.onConnected();
          }
        }

        disconnectedCallback() {
          // Clean up event listeners
          this._eventListeners.forEach(({ target, type, listener, options }) => {
            target.removeEventListener(type, listener, options);
          });
          this._eventListeners = [];
    
          // Any additional cleanup
          if (typeof this.onDisconnected === 'function') {
            this.onDisconnected();
          }
        }

        // Method to add event listeners and track them
        _addEventListener(target, type, listener, options) {
          target.addEventListener(type, listener, options);
          this._eventListeners.push({ target, type, listener, options });
        }
      }

      // Attach static properties to the class
      ComponentClass.templateContent = templateContentClone;
      ComponentClass.bindings = bindings;
      ComponentClass.properties = properties;

      // Define properties on the prototype
      ComponentClass.properties.forEach(varName => {
        Object.defineProperty(ComponentClass.prototype, varName, {
          get: function() {
            return this._propertyValues[varName];
          },
          set: function(newValue) {
            if (this._propertyValues[varName] !== newValue) {
              this._propertyValues[varName] = newValue;
              this._updateProperty(varName);
            }
          },
        });
      });

      // Prepare and execute the scriptFunction once per component
      ComponentClass.scriptFunction = null;
      if (scriptContent.trim()) {
        try {
          // Wrap the script content in a function and execute it in the component's context
          ComponentClass.scriptFunction = new Function(scriptContent);
        } catch (error) {
          console.error(`Error compiling script in component ${name}: ${error.message}`);
        }
      }

      // Register the component
      customElements.define(name, ComponentClass);
    }

    return {
      compileComponent,
    };
  })();

  /**
   * Internal module for loading and parsing HTML files.
   */
  const Loader = (function() {
    /**
     * Loads an HTML file from the given path.
     * @param {string} path - The path to the HTML file (without .html extension).
     * @returns {Promise<string>} - A promise that resolves to the content of the HTML file.
     */
    async function loadFile(path) {
      const fullPath = `${path}.html`;

      try {
        const response = await fetch(fullPath);
        if (!response.ok) {
          throw new Error(`Failed to load: ${fullPath} (Status: ${response.status})`);
        }
        const content = await response.text();
        return content;
      } catch (error) {
        console.error(error.message);
        throw error;
      }
    }

    /**
     * Parses an HTML string into a Document object.
     * @param {string} htmlString - The HTML string to parse.
     * @returns {Document} - The parsed Document object.
     */
    function parseHTML(htmlString) {
      const parser = new DOMParser();
      const doc = parser.parseFromString(htmlString, 'text/html');
      return doc;
    }

    return {
      loadFile,
      parseHTML,
    };
  })();

  /**
   * Global load function.
   * @param {string} path - The path to the HTML file (without .html extension).
   * @returns {Promise<void>}
   */
  window.load = async function(path) {
    console.log(`Loading: ${path}`);

    if (Registry.isFileLoaded(path)) {
      console.log(`Already loaded: ${path}`);
      return;
    }

    try {
      const responseText = await Loader.loadFile(path);
      const doc = Loader.parseHTML(responseText);

      Registry.markFileAsLoaded(path);

      // Extract the <template> with the 'name' attribute
      const template = doc.querySelector('template[name]');
      if (!template) {
        console.error(`No <template name="..."> found in ${path}.html`);
        return;
      }

      const componentName = template.getAttribute('name');
      const templateContent = template.innerHTML;

      // Extract the <script> content
      const script = doc.querySelector('script');
      const scriptContent = script ? script.textContent : '';

      // Use compiler to generate and define the component
      Compiler.compileComponent(componentName, templateContent, scriptContent);

      console.log(`Component registered: ${componentName}`);
    } catch (error) {
      console.error(`Error loading component from ${path}: ${error.message}`);
    }
  };
})();

```

5. Sample component:

```
<!-- app/comp/counter.html -->
<template name="my-counter">
    <style>
        .on {
            background-color: blue;
        }
        .off {
            background-color: aliceblue;
        }
        .btn {
            padding: 20px;
        }
    </style>

    <button class="{status} btn">Count: {count}</button>
</template>

<script>
    this.count = 0;
    this.status = 'on';
    
    const button = this.shadowRoot.querySelector('button');
    const span = button.querySelector('span');

    const component = this; // To maintain correct context inside functions

    function updateCount() {
        component.count++;

        component.status = component.status === 'on' ? 'off' : 'on';
        // The reactive system will automatically update the DOM elements where {count} and {status} are used
    }

    button.addEventListener('click', updateCount);
</script>
```

Your task it's evaluate how efficient and optimized are the components after being compiled, not the compiler, but its output. And compare it, with a compiled component of Svelte. Again, don't compare compilers, type or their performance, but focus exclusively on the output, the compiled component.

You can use as testing sample, the sample component.

Once finished, output the report.