Vue Preprocessor Power-Up

Vue.js is a progressive framework that allows developers to create interactive user interfaces efficiently. Often, to enhance code organization and maintainability, developers leverage preprocessors for templates, scripts, or styles. This challenge focuses on understanding and implementing a basic preprocessor concept within a Vue Single File Component (SFC) structure.

Problem Description

Your task is to create a simplified Vue component that simulates the behavior of a preprocessor. Specifically, you will implement a mechanism that transforms a custom template syntax before it's rendered by Vue. This simulated preprocessor will replace a placeholder with dynamic content based on the component's props or data.

What needs to be achieved:

Implement a Vue component that uses a custom preprocessor for its template. This preprocessor should transform a specific placeholder syntax into actual HTML.

Key requirements:

1. Custom Placeholder: Define a placeholder syntax, e.g., {{ dynamic_variable }}.
2. Preprocessor Logic: Implement a function or method that takes the raw template string as input and returns a transformed string where all occurrences of the custom placeholder are replaced with their corresponding values from the component's context.
3. Vue Component Integration: Create a Vue component where the template is initially defined with these custom placeholders. The component should apply the preprocessor logic to its template before Vue's rendering engine processes it.
4. Dynamic Data: The placeholders should be resolved using data available within the Vue component (e.g., from props or data).

Expected behavior:

When the Vue component renders, the custom placeholders in its template should be dynamically replaced with their actual values. For example, if the template contains Hello, {{ name }}! and the name prop is "World", the rendered output should be "Hello, World!".

Important edge cases to consider:

• Missing data: What happens if a placeholder refers to a variable that doesn't exist in the component's context? (For this challenge, you can assume it resolves to an empty string or a predefined default like "N/A").
• Multiple placeholders: The preprocessor should handle multiple instances of the same or different placeholders within the template.
• Escaping: Consider if there are any characters within the placeholder that might interfere with the parsing (though for this simplified version, we'll assume clean placeholder names).

Examples

Example 1:

Input (Conceptual SFC Template):

<template>
  <div>
    <h1>Welcome, {{ userName }}!</h1>
    <p>Your favorite color is {{ favoriteColor }}.</p>
  </div>
</template>

<script lang="ts">
import { defineComponent } from 'vue';

export default defineComponent({
  props: {
    userName: {
      type: String,
      required: true,
    },
    favoriteColor: {
      type: String,
      default: 'blue',
    },
  },
  // Assume preprocessor logic is applied here before Vue renders
});
</script>

Output (Rendered HTML):

<div>
  <h1>Welcome, Alice!</h1>
  <p>Your favorite color is red.</p>
</div>

Explanation: The userName prop is "Alice" and favoriteColor is "red". The preprocessor logic would have replaced {{ userName }} with "Alice" and {{ favoriteColor }} with "red".

Example 2:

Input (Conceptual SFC Template with missing prop):

<template>
  <div>
    <p>User ID: {{ userId }}</p>
    <p>Status: {{ userStatus }}</p>
  </div>
</template>

<script lang="ts">
import { defineComponent } from 'vue';

export default defineComponent({
  props: {
    userId: {
      type: Number,
      required: true,
    },
  },
  // Assume preprocessor logic is applied here
});
</script>

Output (Rendered HTML):

<div>
  <p>User ID: 12345</p>
  <p>Status: N/A</p>
</div>

Explanation: The userId prop is 12345. The userStatus prop is not provided and doesn't have a default. The preprocessor resolves {{ userId }} to "12345" and {{ userStatus }} to "N/A" (our chosen default for missing values).

Constraints

• The preprocessor logic must be implemented in TypeScript.
• The placeholder format will strictly be {{ variableName }}.
• The component context (props and data) will be accessible within the preprocessor logic.
• For this challenge, you can assume the preprocessor will be applied once to the entire template string. You do not need to worry about complex nested structures or dynamic template updates after initial rendering.

Notes

Think about how you can intercept or modify the template content before Vue's compiler parses it. You might consider a custom Vue plugin or a build-time transformation approach conceptually, but for the purpose of demonstrating the logic, you can simulate this within the component itself, perhaps by having a method that returns the preprocessed template string or by manually applying the transformation to the template before it's passed to Vue's compiler (though the latter is harder to show directly in a standard SFC without build tools).

A good approach would be to create a helper function that takes the template string and the component's context (props, data) and returns the transformed string. You can then conceptually imagine this function being called by a hypothetical preprocessor hook in Vue.

Consider using regular expressions to find and replace your custom placeholders.