Vue Static Hoisting Implementation Challenge

This challenge focuses on understanding and implementing a core Vue.js optimization technique: static hoisting. You will learn how Vue identifies and optimizes static parts of your template, leading to improved performance by avoiding unnecessary DOM updates and re-renders. Your task is to simulate this process by creating a mechanism that can hoist static content from a Vue-like template structure.

Problem Description

Vue.js performs an optimization called "static hoisting" for parts of the template that are determined to be static (i.e., they don't change during the component's lifecycle). This means these static elements and their attributes are processed only once during the initial render and are not re-checked during subsequent updates.

Your goal is to implement a simplified version of this static hoisting mechanism. You will be given a representation of a Vue template (using a basic Abstract Syntax Tree or AST-like structure) and you need to identify and "hoist" the static nodes. Hoisting means creating a separate representation for these static parts that can be reused.

Key Requirements:

• Node Representation: You'll need a way to represent template nodes. This can include elements, text nodes, and potentially attributes.
• Static Identification: Develop logic to determine if a node and its children are static. A node is considered static if it, and all its descendants, have no dynamic bindings (like v-bind:class, {{ dynamic }}, v-model, etc.).
• Hoisting Mechanism: Implement a process that takes the template AST and returns:
  • The optimized template AST, where static subtrees are replaced by references to hoisted static VNodes.
  • A list of the hoisted static VNodes.
• VNode Representation: You should define a VNode (Virtual Node) structure to represent the rendered output. This VNode should clearly distinguish between static and dynamic parts.

Expected Behavior:

The hoisting process should correctly identify subtrees that are entirely static. These static subtrees should be moved to a separate list of hoisted VNodes. In the main template AST, the original static subtree should be replaced with a placeholder that references its corresponding hoisted VNode.

Edge Cases:

• Templates with only static content.
• Templates with only dynamic content.
• Mixed static and dynamic content.
• Empty templates.
• Nodes with attributes that are static (e.g., id="my-id").
• Nodes with attributes that are dynamic (e.g., :class="dynamicClass").
• Text nodes containing only static text.
• Text nodes containing dynamic interpolations ({{ myVar }}).

Examples

Example 1:

Input: A template AST representing:

<div id="static-div">
  Hello, {{ name }}!
  <p>This is static text.</p>
</div>

Output:

• Hoisted VNodes:

  [
    {
      "type": "element",
      "tag": "p",
      "props": {},
      "children": [
        { "type": "text", "content": "This is static text." }
      ]
    }
  ]
  

• Optimized Template AST:

  {
    "type": "element",
    "tag": "div",
    "props": { "id": "static-div" },
    "children": [
      { "type": "text", "content": "Hello, ", "isStatic": false },
      { "type": "interpolations", "content": "name", "isStatic": false },
      { "type": "text", "content": "!", "isStatic": false },
      { "type": "staticNode", "index": 0 } // Reference to the first hoisted node
    ]
  }
  

Explanation: The <p> element and its text child are entirely static. They are extracted into the hoistedVnodes array. The original position in the template is replaced by a staticNode reference. The div and its text parts are considered dynamic due to the interpolation.

Example 2:

Input: A template AST representing:

<div>
  <span class="fixed">Static Span</span>
</div>

Output:

• Hoisted VNodes:

  [
    {
      "type": "element",
      "tag": "span",
      "props": { "class": "fixed" },
      "children": [
        { "type": "text", "content": "Static Span" }
      ]
    }
  ]
  

• Optimized Template AST:

  {
    "type": "element",
    "tag": "div",
    "props": {},
    "children": [
      { "type": "staticNode", "index": 0 } // Reference to the first hoisted node
    ]
  }
  

Explanation: The entire <span> subtree is static, including its attribute and text content. It is hoisted. The div is now considered static because its only child is a hoisted static node.

Example 3: Nested Static Content

Input: A template AST representing:

<section>
  <h1>Title</h1>
  <p>Some intro</p>
  <div :class="dynamicClass">
    <img src="/static/logo.png" alt="Logo">
  </div>
</section>

Output:

• Hoisted VNodes:

  [
    {
      "type": "element",
      "tag": "img",
      "props": { "src": "/static/logo.png", "alt": "Logo" },
      "children": []
    }
  ]
  

• Optimized Template AST:

  {
    "type": "element",
    "tag": "section",
    "props": {},
    "children": [
      {
        "type": "element",
        "tag": "h1",
        "props": {},
        "children": [{ "type": "text", "content": "Title" }]
      },
      {
        "type": "element",
        "tag": "p",
        "props": {},
        "children": [{ "type": "text", "content": "Some intro" }]
      },
      {
        "type": "element",
        "tag": "div",
        "props": { ":class": "dynamicClass" }, // This attribute makes the div dynamic
        "children": [
          { "type": "staticNode", "index": 0 } // Reference to the hoisted img
        ]
      }
    ]
  }
  

Explanation: The <img> is static and is hoisted. The <section>, <h1>, and <p> are also static. The <div> is dynamic because of :class. Therefore, only the <img> subtree is moved to hoistedVnodes. The div's children are updated to reference the hoisted node.

Constraints

• Node Structure: Assume nodes have properties like type (e.g., 'element', 'text', 'interpolation'), tag (for elements), content (for text/interpolation), props (an object of key-value pairs), and children (an array of nodes). Dynamic bindings will be represented with a prefix like : (e.g., :class, :id).
• Template Depth: The maximum depth of nested elements will not exceed 15.
• Number of Nodes: A single template will contain a maximum of 100 nodes.
• Performance: The hoisting process should be reasonably efficient, ideally with a time complexity close to O(N), where N is the number of nodes in the template.

Notes

• Consider how you will represent the distinction between static and dynamic attributes. A simple approach is to look for prefixes like :.
• Think about the recursive nature of identifying static subtrees. If a parent node has a dynamic child or dynamic attribute, the parent itself is not considered static, even if some of its children might be.
• Your VNode representation for hoisted nodes should be immutable.
• You can define your own types for the AST nodes and the VNode structure. Focus on the logic of identification and transformation.
• This challenge is about understanding the principle of static hoisting. A full Vue compiler involves much more complexity.