Implement v-on Shorthand in Vue (Vue 3 / TypeScript)

Vue's directive system provides powerful ways to bind data and behavior to your HTML. One common directive is v-on, used for listening to DOM events. This challenge asks you to implement a core feature that simplifies event handling: the @ shorthand for v-on. Mastering this will streamline your Vue development by reducing boilerplate code.

Problem Description

Your task is to create a mechanism within a simplified Vue-like rendering system that recognizes and correctly interprets the @ shorthand for the v-on directive. This means that when a template contains an attribute like @click="handleClick", your system should treat it as if it were v-on:click="handleClick".

Key Requirements:

1. Directive Parsing: Your system must be able to parse template attributes.
2. Shorthand Recognition: It should identify attributes starting with @ as event listeners.
3. Directive Transformation: The @ shorthand should be transformed into the full v-on: syntax internally before being processed by the Vue runtime (or our simulated runtime).
4. Event Binding: The specified event listener (e.g., handleClick) should be correctly bound to the corresponding DOM event (e.g., click).

Expected Behavior:

When a component is rendered with an element containing an attribute like @click="someMethod", the someMethod function should be invoked when the click event occurs on that element.

Edge Cases:

• Multiple Event Listeners: An element might have multiple event listeners defined, some using the shorthand, some using the full syntax.
• No Event Listeners: An element might have no event listeners.
• Invalid Shorthand: Consider what happens if an attribute looks like shorthand but isn't a valid event (though for this challenge, we'll assume valid event names after @).

Examples

Example 1:

// Simplified Vue Component Structure
interface ComponentOptions {
  template: string;
  methods?: { [key: string]: Function };
}

interface MockElement {
  tagName: string;
  attributes: { [key: string]: string };
  listeners: { [key: string]: Function };
  // ... other properties for simulation
}

function mountComponent(options: ComponentOptions): { element: MockElement } {
  // ... rendering logic that parses template and binds directives
  // This function should internally handle the @ shorthand
  return { /* ... */ };
}

const component = mountComponent({
  template: '<button @click="increment">Click Me</button>',
  methods: {
    increment() {
      console.log('Button clicked!');
    }
  }
});

// Simulate a click event on the button
// component.element.attributes['@click'] should have been processed to
// component.element.listeners['click'] = component.methods.increment
// component.element.dispatchEvent('click'); // This would trigger the log

Output (simulated console log):

Button clicked!

Explanation:

The template <button @click="increment">Click Me</button> contains the @click shorthand. The mountComponent function recognizes this, transforms it internally to v-on:click="increment", and binds the increment method from the methods object to the button's click event. When the event is dispatched, the increment function executes.

Example 2:

const component = mountComponent({
  template: `
    <div>
      <p @mouseover="showTooltip" v-on:mouseleave="hideTooltip">Hover Over Me</p>
    </div>
  `,
  methods: {
    showTooltip() {
      console.log('Tooltip shown');
    },
    hideTooltip() {
      console.log('Tooltip hidden');
    }
  }
});

// Simulate events
// component.element.dispatchEvent('mouseover'); // would trigger showTooltip
// component.element.dispatchEvent('mouseleave'); // would trigger hideTooltip

Output (simulated console logs):

Tooltip shown
Tooltip hidden

Explanation:

This example demonstrates that the system can handle both the @ shorthand and the full v-on: syntax on the same element, and that the parsing logic correctly identifies and processes both.

Constraints

• You will be working with a simulated Vue rendering environment. You do not need to build a full Vue compiler or runtime from scratch. Focus on the directive parsing and transformation logic.
• The input will be a string representing a simple HTML template with attributes.
• Event handler names in the template will be valid JavaScript identifiers.
• You can assume that method names in the methods object will directly correspond to the handler names in the template.
• Performance is not a primary concern for this challenge, but your solution should be reasonably efficient.

Notes

Consider how you might parse the template string to identify attributes. You'll likely need to extract attribute names and their values. When you encounter an attribute name that starts with @, you'll need to transform it into the v-on: format before associating the handler function with the appropriate event. Think about how you would represent the element and its event listeners in your simulated environment.