# JQHTML v2 Complete Syntax & Instruction Format Specification

## Overview

JQHTML v2 is a composable component templating language for jQuery that compiles to efficient JavaScript instruction arrays. This document defines the complete syntax specification and the instruction format that templates compile to.

## Critical Concepts

### The Instruction Array Pattern

Templates compile to functions that return arrays of rendering instructions:

```javascript
// Every template function returns this structure:
function render(Component, data, args, content) {
  const _output = [];  // Instruction array
  // ... push instructions ...
  return [_output, this];  // CRITICAL: Returns tuple [instructions, context]
}
```

### Why This Pattern Exists

1. **Deferred Execution**: Instructions can be processed when optimal
2. **Single DOM Write**: All HTML built as string, then one `$.html()` call
3. **Complex Attribute Handling**: Functions and objects can't go in HTML strings
4. **Component Coordination**: Parent/child relationships preserved through execution

## Template Syntax

### 1. Component Definition

Components are defined using the `<Define:>` tag:

```jqhtml
<Define:ComponentName>
  <!-- Component template -->
</Define:ComponentName>
```

### 2. $ Attribute System

JQHTML uses the `$` prefix for passing data to components as `this.args`:

#### Syntax Rules

1. **Quoted = Literal String**
   ```jqhtml
   $title="User Profile"    → args.title = "User Profile"
   $expr="this.user"        → args.expr = "this.user" (the string, not evaluated!)
   ```

2. **Unquoted = JavaScript Expression**
   ```jqhtml
   $user=this.user          → args.user = {actual user object}
   $count=42                → args.count = 42
   $enabled=true            → args.enabled = true
   $handler=this.onClick    → args.handler = function reference
   ```

3. **Parentheses for Complex Expressions**
   ```jqhtml
   $status=(active ? 'online' : 'offline')
   $data=({...this.user, modified: true})
   $items=(this.data.items || [])
   ```

#### Runtime Behavior

- All $ attributes become properties in `this.args` (NOT `this.data`)
- Stringable values (strings/numbers) appear as `data-*` DOM attributes
- Complex values (objects/arrays/functions) accessible only via `this.args`
- Component constructor syncs stringable args to DOM

#### Example

```jqhtml
<!-- Parent component with this.user = {name: "Alice", id: 123} -->
<UserCard
  $user=this.user           <!-- args.user = {name: "Alice", id: 123} -->
  $title="User Profile"      <!-- args.title = "User Profile" -->
  $count=42                  <!-- args.count = 42 -->
  data-role="admin"          <!-- args.role = "admin" -->
/>
```

Result in UserCard component:
- `this.args.user` = {name: "Alice", id: 123} (object)
- `this.args.title` = "User Profile" (string)
- `this.args.count` = 42 (number)
- `this.args.role` = "admin" (from data- attribute)

DOM shows: `<div data-title="User Profile" data-count="42" data-role="admin">` (no data-user since it's an object)

### 3. Expressions

Output JavaScript expressions using `<%= %>` (escaped) or `<%!= %>` (unescaped):

```jqhtml
<%= this.data.title %>                    <!-- Escaped output -->
<%!= this.data.rawHtml %>                 <!-- Unescaped output -->
<%@= this.data.maybeUndefined %>          <!-- Escaped with error suppression -->
<%!@= this.data.maybeUndefinedHtml %>     <!-- Unescaped with error suppression -->
```

### 3. Code Blocks

Execute JavaScript code using `<% %>`. Regular JavaScript passes through unchanged:

```jqhtml
<% const items = this.data.items || []; %>
<% console.log('Rendering:', items.length); %>

<!-- Regular JavaScript control flow -->
<% if (condition) { %>
  <p>True branch</p>
<% } else { %>
  <p>False branch</p>
<% } %>

<% for (const item of items) { %>
  <div><%= item.name %></div>
<% } %>
```

**Design Rationale**: JavaScript code blocks pass through directly into the generated function. This allows developers to use any JavaScript construct without parser limitations.

## Component Invocation

### Basic Component Usage

Components are invoked using capital-letter tags:

```jqhtml
<UserCard />                              <!-- Self-closing, no content -->
<UserCard></UserCard>                    <!-- Empty paired tags, no content -->
<UserCard>Default content</UserCard>      <!-- With innerHTML content (most common) -->
```

### Property Passing

```jqhtml
<!-- String literals -->
<UserCard name="John Doe" role="admin" />

<!-- String interpolation -->
<UserCard title="Welcome <%= this.data.userName %>!" />
<div class="card <%= this.data.active ? 'active' : '' %>">

<!-- Data attributes ($property syntax) -->
<UserCard $user=this.data.currentUser $active=true />
<!-- Compiles to: data-user and data-active attributes -->

<!-- Property binding (:property syntax) -->
<UserCard :user="currentUser" :settings="{ theme: 'dark' }" />
<!-- Compiles to: data-bind-user and data-bind-settings attributes -->

<!-- Event binding (@event syntax) -->
<UserCard @save="handleSave" @cancel="() => closeModal()" />
<!-- Compiles to: data-on-save and data-on-cancel attributes -->
```

### $ Attribute System

JQHTML uses the `$` prefix as a shorthand for data attributes with special handling:

#### General Case: `$foo="bar"` → `data-foo`

```jqhtml
<div $user=currentUser $theme="dark" $count=42>
<!-- Compiles to: -->
{tag: ["div", {"data-user": currentUser, "data-theme": "dark", "data-count": 42}, false]}
```

**Runtime Behavior**:
1. The attribute is set via jQuery's `.data()` method: `$element.data('user', currentUser)`
2. For debugging visibility, if the value is a string or number, it's also set as a DOM attribute
3. Objects and arrays are stored in `.data()` but not visible in DOM

#### Special Case: `$sid="name"` → Scoped IDs

The `$sid` attribute has special handling for component-scoped element selection:

```jqhtml
<Define:UserCard>
  <div $sid="container">
    <input $sid="username" type="text" />
    <button $sid="submit">Submit</button>
  </div>
</Define:UserCard>
```

**Compilation**:
```javascript
// In render function (receives _cid parameter)
function render(_cid) {
  const _output = [];
  _output.push({tag: ["div", {"id": "container:" + _cid}, false]});
  _output.push({tag: ["input", {"id": "username:" + _cid, "type": "text"}, false]});
  _output.push({tag: ["button", {"id": "submit:" + _cid}, false]});
  // ...
}
```

**Runtime Usage**:
```javascript
class UserCard extends Component {
  init() {
    // Find scoped elements
    const $username = this.$sid('username');  // Returns $('#username:123')
    const $submit = this.$sid('submit');      // Returns $('#submit:123')
    
    $submit.on('click', () => {
      const value = $username.val();
      // ...
    });
  }
}
```

#### Lexical Scoping of `_cid`

Component IDs flow through lexical scope naturally:

```jqhtml
<Define:ParentComponent>
  <div $sid="parent-element">        <!-- Gets ParentComponent's _cid -->
    <ChildComponent>
      <div $sid="slot-element" />    <!-- Also gets ParentComponent's _cid -->
    </ChildComponent>
  </div>
</Define:ParentComponent>

<Define:ChildComponent>
  <div $sid="child-element">         <!-- Gets ChildComponent's _cid -->
    <%= content() %>                <!-- Slot content preserves parent's _cid -->
  </div>
</Define:ChildComponent>
```

This happens because content functions capture their defining scope:
```javascript
// ParentComponent render
function render(_cid) {  // Parent's _cid = 123
  _output.push({comp: ["ChildComponent", {}, () => {
    // This arrow function captures Parent's _cid
    const _output = [];
    _output.push({tag: ["div", {"id": "slot-element:" + _cid}, false]});  // slot-element:123
    return [_output, this];
  }]});
}

// ChildComponent render  
function render(_cid) {  // Child's _cid = 456
  _output.push({tag: ["div", {"id": "child-element:" + _cid}, false]});  // child-element:456
}
```

#### Attribute Value Interpolation

Within quoted attribute values, `<%= %>` and `<%!= %>` perform string interpolation:

```jqhtml
<!-- Both of these work identically in attributes -->
<div title="User: <%= user.name %>">
<div title="User: <%!= user.name %>">

<!-- Compiles to -->
{tag: ["div", {"title": "User: " + user.name}, false]}
```

**Design Rationale**: Inside attribute values, HTML escaping is inappropriate because we're building a JavaScript string, not HTML content. The JavaScript string serialization handles all necessary escaping (quotes, backslashes, etc.). This is semantically different from top-level `<%= %>` which outputs to HTML and requires escaping.

## Binding Syntax (v2)

### Property Binding with `:`

The `:` prefix creates dynamic property bindings that are always evaluated as JavaScript expressions:

```jqhtml
<!-- Simple property binding -->
<input :value="formData.name" :disabled="isLoading" />

<!-- Complex expressions -->
<div :style="{ color: textColor, fontSize: size + 'px' }" />

<!-- Method calls -->
<select :options="getOptions(category)" />
```

**Compilation**:
- `:prop="expr"` → `{"data-bind-prop": expr}` (no quotes around expr)
- Values are ALWAYS treated as JavaScript expressions
- Even quoted strings like `:prop="value"` become expressions

### Event Binding with `@`

The `@` prefix binds event handlers:

```jqhtml
<!-- Simple handler -->
<button @click="handleClick">Click Me</button>

<!-- With arguments -->
<button @click="deleteItem(item.id)">Delete</button>

<!-- Inline arrow function -->
<input @input="(e) => updateValue(e.target.value)" />

<!-- Multiple events -->
<form @submit="save" @reset="clear">
```

**Compilation**:
- `@event="handler"` → `{"data-on-event": handler}`
- Handlers are JavaScript expressions (function references or inline functions)

### Binding Design Rationale

1. **Vue.js Familiarity**: Uses the same `:prop` and `@event` syntax as Vue.js
2. **Always Expressions**: Unlike `$` attributes which distinguish strings vs expressions, bindings are ALWAYS expressions
3. **Runtime Processing**: The runtime will need to handle these specially:
   - `data-bind-*` attributes set properties dynamically
   - `data-on-*` attributes attach event listeners
4. **Separate from `$` System**: Bindings serve a different purpose than data attributes

## Component Content & innerHTML (Primary Pattern)

### Using `content()` Function - The Most Common Approach

**The vast majority of components will use the simple `content()` function to output innerHTML passed by parent components.** This is the primary, recommended pattern for component composition:

```jqhtml
<!-- Define a component that outputs innerHTML -->
<Define:Container>
  <div class="container">
    <div class="container-body">
      <%= content() %>  <!-- Outputs whatever innerHTML was passed -->
    </div>
  </div>
</Define:Container>

<!-- Usage - just pass innerHTML like regular HTML -->
<Container>
  <p>This is the content</p>
  <span>More content here</span>
  <!-- Any HTML/components can go here -->
</Container>
```

### Common Patterns with `content()`

```jqhtml
<!-- Card component with innerHTML -->
<Define:Card>
  <div class="card">
    <div class="card-body">
      <%= content() %>  <!-- Simple innerHTML output -->
    </div>
  </div>
</Define:Card>

<!-- Panel with conditional innerHTML -->
<Define:Panel>
  <div class="panel">
    <% if (this.args.title): %>
      <div class="panel-header"><%= this.args.title %></div>
    <% endif; %>
    <div class="panel-body">
      <%= content() %>
    </div>
  </div>
</Define:Panel>

<!-- Wrapper that adds behavior to innerHTML -->
<Define:Collapsible>
  <div class="collapsible" $sid="wrapper">
    <button $onclick="toggle">Toggle</button>
    <div class="content" $sid="content">
      <%= content() %>  <!-- Wrapped innerHTML -->
    </div>
  </div>
</Define:Collapsible>
```

### How `content()` Works

1. **Parent passes innerHTML**: When invoking `<Component>innerHTML here</Component>`
2. **Template receives it**: The `content` parameter in render function contains the innerHTML
3. **Output with `<%= content() %>`**: Call the function to output the HTML where needed
4. **No special syntax needed**: Just regular HTML/components as children

### Important Rules

- **No mixing**: If a component uses ANY slots (`<#slotname>`), ALL content must be in slots
- **Most components don't need slots**: The simple `content()` pattern handles 95% of use cases
- **Slots are for advanced scenarios**: Only use slots when you need multiple named content areas

## Slot System (Advanced Feature)

**Note: Slots are an advanced feature for specific use cases. Most components should use the simpler `content()` pattern shown above.**

### When to Use Slots vs `content()`

Use `content()` (recommended for most cases):
- Single content area
- Wrapping/decorating content
- Simple component composition
- Standard container components

Use slots (advanced cases only):
- Multiple distinct content areas (header/body/footer)
- Complex layouts with specific placement
- Data table templates with row/header/footer sections

### 1. Named Slots

Pass content to specific slots using `<#slotname>` syntax:

```jqhtml
<DataTable $items=this.data.users>
  <#header>
    <th>ID</th>
    <th>Name</th>
    <th>Email</th>
  </#header>
  
  <#row>
    <td><%= row.id %></td>
    <td><%= row.name %></td>
    <td><%= row.email %></td>
  </#row>
  
  <#empty />  <!-- Self-closing slot -->
</DataTable>
```

### 2. Accessing Slots in Components (Advanced)

For the rare cases where slots are needed, components can check for and render specific named slots:

```jqhtml
<Define:Card>
  <div class="card">
    <!-- Render default slot -->
    <%= content() %>
    
    <!-- Render named slot -->
    <% if (content('footer')) { %>
      <footer>
        <%= content('footer', { timestamp: new Date() }) %>
      </footer>
    <% } %>
  </div>
</Define:Card>
```

## Instruction Format Reference

### Instruction Types

Templates compile to three instruction types:

1. **`{tag: [...]}`** - HTML elements
2. **`{comp: [...]}`** - Component invocations
3. **`{slot: [...]}`** - Slot definitions

### 1. Tag Instruction

```javascript
{tag: [tagname, attributes, self_closing]}
```

**Format:**
- `tagname`: String - HTML tag name
- `attributes`: Object - Tag attributes (may contain functions!)
- `self_closing`: Boolean - Whether tag self-closes

**Examples:**
```javascript
{tag: ["div", {"class": "user-card"}, false]}
{tag: ["img", {"src": "/avatar.jpg", "alt": "User"}, true]}
{tag: ["button", {"onclick": this.handleClick}, false]}
{tag: ["div", {"data-sid": "header"}, false]}  // $sid becomes data-id
```

### 2. Component Instruction

```javascript
{comp: [component_name, attributes, optional_innerhtml_function]}
```

**Format:**
- `component_name`: String - Component to instantiate
- `attributes`: Object - Props/attributes to pass
- `optional_innerhtml_function`: Function - Contains slots and default content

**CRITICAL**: When a component invocation contains slots or any child content, it MUST use the three-parameter form with a content function. Slots are NOT separate instructions after the component - they are contained within the component's content function.

**Examples:**
```javascript
// Simple component (no children)
{comp: ["UserAvatar", {"data-userId": this.data.id}]}

// Component with slots
{comp: ["DataTable", {"data-rows": this.data.items}, (DataTable) => {
  const _output = [];
  _output.push({slot: ["header", {}, (header) => {
    const _output = [];
    _output.push({tag: ["th", {}, false]});
    _output.push("Name");
    _output.push("</th>");
    return [_output, this];
  }]});
  return [_output, this];
}]}
```

### 3. Slot Instruction

```javascript
{slot: [slot_name, attributes, render_function]}
```

**Format:**
- `slot_name`: String - Slot identifier
- `attributes`: Object - Props for slot
- `render_function`: Function - Returns `[instructions, context]`

**Example:**
```javascript
{slot: ["actions", {}, (actions) => {
  const _output = [];
  _output.push({tag: ["button", {"onclick": this.delete}, false]});
  _output.push("Delete");
  _output.push("</button>");
  return [_output, this];
}]}
```

### 4. String Output

Raw strings are pushed directly:

```javascript
_output.push({tag: ["div", {}, false]});  // Opening tag (instruction)
_output.push("Hello, ");                  // Raw text
_output.push(html(this.data.name));       // Escaped text
_output.push("</div>");                   // Closing tag (raw string!)
```

**CRITICAL**: Closing tags are ALWAYS raw strings, not instructions.

## Context Preservation

### v1 Pattern: `_that = this`

The v1 pattern preserves component context through nested functions:

```javascript
function render(Component, data, args, content) {
  let _that = this;  // Preserve component instance
  let _output = [];
  
  _output.push({comp: ["Child", {}, function(Child) {
    let _output = [];
    // _that still refers to parent component
    _output.push(html(_that.data.value));
    return [_output, _that];
  }.bind(_that)]});
  
  return [_output, _that];
}
```

### v2 Pattern: Arrow Functions

v2 uses arrow functions for natural context preservation:

```javascript
function render(Component, data, args, content) {
  const _output = [];
  
  _output.push({comp: ["Child", {}, (Child) => {
    const _output = [];
    // 'this' refers to parent component naturally
    _output.push(html(this.data.value));
    return [_output, this];
  }]});
  
  return [_output, this];
}
```

## Runtime Processing

### Phase 1: Instruction Execution

```javascript
let [instructions, context] = template.render.bind(component)(
  component,
  component.data,
  args,
  content_fn
);
```

### Phase 2: Instruction Processing

1. **Build HTML**: Process all string and simple tag instructions
2. **Track Complex Elements**: Store elements with function attributes
3. **Single DOM Write**: `component.$.html(html.join(''))`
4. **Apply Attributes**: Attach event handlers and complex attributes
5. **Initialize Components**: Create child component instances

## Self-Closing HTML Tags

The following HTML tags are automatically treated as self-closing:
- `area`, `base`, `br`, `col`, `embed`, `hr`, `img`, `input`
- `link`, `meta`, `param`, `source`, `track`, `wbr`

## Complete Example

### Template

```jqhtml
<Define:UserDashboard>
  <div class="dashboard">
    <Header $title="User Management">
      <#actions>
        <button $onclick=this.addUser>Add User</button>
      </#actions>
    </Header>
    
    <% if (this.data.loading): %>
      <LoadingSpinner />
    <% else: %>
      <UserTable $users=this.data.users>
        <#header>
          <th>ID</th>
          <th>Name</th>
          <th>Actions</th>
        </#header>
        
        <#row>
          <td><%= row.id %></td>
          <td><%= row.name %></td>
          <td>
            <button $onclick=this.editUser>Edit</button>
          </td>
        </#row>
      </UserTable>
    <% endif; %>
  </div>
</Define:UserDashboard>
```

### Compiled Output Structure

```javascript
function render(Component, data, args, content) {
  const _output = [];
  
  _output.push({tag: ["div", {"class": "dashboard"}, false]});
  
  // Header component with slots
  _output.push({comp: ["Header", {"data-title": "User Management"}, (Header) => {
    const _output = [];
    _output.push({slot: ["actions", {}, (actions) => {
      const _output = [];
      _output.push({tag: ["button", {"data-onclick": this.addUser}, false]});
      _output.push("Add User");
      _output.push("</button>");
      return [_output, this];
    }]});
    return [_output, this];
  }]});
  
  // ... rest of compilation
  
  _output.push("</div>");
  return [_output, this];
}
```

## Component CSS Classes

When components are rendered, the runtime automatically applies CSS classes based on the component's inheritance hierarchy:

```html
<!-- For a UserCard extending BaseCard extending Component -->
<div class="UserCard BaseCard Component" ...>
```

This enables CSS targeting at any level of the hierarchy:
```css
.Component { /* all components */ }
.UserCard { /* specific component type */ }
.BaseCard { /* all cards */ }
```

**Implementation Note**: The Component base class automatically applies these classes during initialization. This feature works regardless of minification since class names are preserved through the component's constructor name.

## Critical Implementation Rules

### What MUST Be Preserved

1. **Instruction Array Structure**: The `{tag:...}`, `{comp:...}`, `{slot:...}` format
2. **Return Tuple**: Functions MUST return `[instructions, context]`
3. **Deferred Component Init**: Components render as placeholders first
4. **Single DOM Write**: Build all HTML, write once
5. **Content Function**: Parent components receive content function to access slots

### Common Pitfalls

1. **Forgetting Return Format**: Must return `[array, context]`, not just array
2. **String vs Instruction**: Closing tags are strings, opening tags are instructions
3. **Context Loss**: Without proper binding, nested functions lose component reference
4. **Direct DOM Manipulation**: Never manipulate DOM during instruction building
5. **Missing html() Escaping**: User content must be escaped
6. **Slots Outside Components**: Slots must be inside component content functions