Element Library: Programmatic HTML Generation in Go

A comprehensive guide to using github.com/rohanthewiz/element for building HTML without templates.

Overview

Element is a Go library that generates HTML programmatically by leveraging Go's natural function execution order. Instead of templates, you write Go code that mirrors HTML's tree structure.

Key Insight: When you call a builder method like b.Div(), the opening tag <div> is written immediately to an internal buffer. The element returned must be terminated with R(), T(), or F() to write the closing tag.

---

Getting Started

Creating a Builder

Start with a builder for creating elements

import "github.com/rohanthewiz/element"

// Method 1: Standard creation
b := element.NewBuilder()

// Method 2: Shorthand
b := element.B()

// Method 3: From pool (high-throughput HTTP handlers)
b := element.AcquireBuilder()
defer element.ReleaseBuilder(b)

The Critical Concept: Immediate Tag Writing

When you call an element method, the opening tag is written immediately:

b := element.NewBuilder()
b.Div("id", "container")  // "<div id="container">" is NOW in the buffer
// The element is returned, waiting for termination

This is why Element works - Go's function argument evaluation order means children are processed (and their tags written) before the parent's R() closes the parent tag.

---

Termination Methods

Every non-self-closing element must be terminated. This writes the closing tag.

R() - Render with Children

Use when the element has child elements, mixed content, or no children:

// With child elements
b.Div().R(
    b.P().T("First paragraph"),
    b.P().T("Second paragraph"),
)
// Output: <div><p>First paragraph</p><p>Second paragraph</p></div>

// Empty element
b.Div().R()
// Output: <div></div>

T() - Text Only

Use when the element contains only text (most efficient for text-only):

b.P().T("Hello, World!")
// Output: <p>Hello, World!</p>

// Multiple strings are concatenated
b.Span().T("Hello", " ", "World")
// Output: <span>Hello World</span>

F() - Formatted Text

Use for fmt.Sprintf-style formatted text:

count := 42
b.P().F("You have %d items", count)
// Output: <p>You have 42 items</p>

Self-Closing Elements

Elements like <br>, <img>, <input>, <hr>, <meta> don't require termination, but you can call R() for consistency:

b.Br()                              // <br>
b.Img("src", "logo.png", "alt", "Logo")  // <img src="logo.png" alt="Logo">
b.Input("type", "text", "name", "email") // <input type="text" name="email">

// R() is safe to call on single-tag elements (does nothing extra)
b.Br().R()  // Still just <br>

---

Attributes

Attributes are passed as key-value string pairs:

// Multiple attributes
b.Div("id", "main", "class", "container", "data-role", "content").R()
// Output: <div id="main" class="container" data-role="content"></div>

// Using Class convenience methods (cleaner for class attribute)
b.DivClass("container", "id", "main").R()
// Output: <div class="container" id="main"></div>

Important: Always provide an even number of attribute strings. In debug mode, an odd count triggers a warning and the last value is dropped.

---

Class Convenience Methods

Over 90 elements have *Class methods that accept class as the first attribute:

// Instead of:
b.Div("class", "card").R()
b.P("class", "intro").R()
b.Button("class", "btn primary", "type", "submit").R()

// Use:
b.DivClass("card").R()
b.PClass("intro").R()
b.ButtonClass("btn primary", "type", "submit").R()

---

Building Complex Structures

Nesting Elements

Go's function execution order makes nesting natural:

b.Html().R(
    b.Head().R(
        b.Title().T("My Page"),
        b.Meta("charset", "utf-8"),
    ),
    b.Body().R(
        b.DivClass("container").R(
            b.H1().T("Welcome"),
            b.PClass("intro").R(
                b.T("This is "),
                b.SpanClass("highlight").T("important"),
                b.T(" content."),
            ),
        ),
    ),
)

Using Wrap() for Logic

Wrap() allows arbitrary Go code within the render tree:

b.Div().R(
    b.H2().T("Items"),
    b.Wrap(func() {
        if len(items) == 0 {
            b.P().T("No items found")
        } else {
            for _, item := range items {
                b.P().T(item)
            }
        }
    }),
)

Using ForEach() for Iteration

ForEach is a generic helper for iterating slices:

items := []string{"Apple", "Banana", "Cherry"}

b.Ul().R(
    element.ForEach(items, func(item string) {
        b.Li().T(item)
    }),
)
// Output: <ul><li>Apple</li><li>Banana</li><li>Cherry</li></ul>

Using b.T() for Direct Text

b.T() writes text directly to the builder (outside element context):

b.P().R(
    b.T("Start of paragraph. "),
    b.Strong().T("Bold text"),
    b.T(" End of paragraph."),
)

---

Components

Components are reusable HTML fragments implementing the Component interface:

type Component interface {
    Render(b *element.Builder) (x any)
}

Creating a Component

type Card struct {
    Title   string
    Content string
}

func (c Card) Render(b *element.Builder) (x any) {
    b.DivClass("card").R(
        b.H3().T(c.Title),
        b.P().T(c.Content),
    )
    return
}

Using Components

// Method 1: Direct render call
card := Card{Title: "Hello", Content: "World"}
b.Div().R(
    card.Render(b),
)

// Method 2: RenderComponents for multiple
cards := []element.Component{
    Card{Title: "One", Content: "First"},
    Card{Title: "Two", Content: "Second"},
}
b.Div().R(
    element.RenderComponents(b, cards...),
)

HtmlPage Helper

For complete HTML documents with a body component:

type PageBody struct {
    Title string
}

func (pb PageBody) Render(b *element.Builder) (x any) {
    b.H1().T(pb.Title)
    b.P().T("Welcome to the page")
    return
}

func generatePage() string {
    b := element.B()
    b.HtmlPage(
        "body { font-family: sans-serif; }",  // CSS
        "<title>My Page</title>",              // Head content
        PageBody{Title: "Home"},               // Body component
    )
    return b.String()
}

---

Builder Pool for High-Throughput

In HTTP handlers processing many requests, use the builder pool to reduce GC pressure:

func handler(w http.ResponseWriter, r *http.Request) {
    b := element.AcquireBuilder()
    defer element.ReleaseBuilder(b)

    b.Html().R(
        b.Body().R(
            b.H1().T("Hello"),
        ),
    )

    w.Header().Set("Content-Type", "text/html; charset=utf-8")
    w.Write(b.Bytes())  // Use Bytes() to avoid string allocation
}

When to use pooling:

• High-traffic HTTP handlers
• Server-side rendering APIs
• Any scenario creating many short-lived builders

When pooling isn't needed:

• CLI tools, batch processing
• Low-traffic applications
• One-off page generation

---

Debug Mode

Debug mode helps catch malformed HTML during development:

// Enable debug mode
element.DebugSet()

// Check for issues
html := element.DebugShow()

// Clear debug mode
element.DebugClear()

Debug mode detects:

• Unclosed tags
• Odd number of attributes
• Children on self-closing elements
• Unwrapped text content

---

Output Methods

b := element.NewBuilder()
// ... build HTML ...

// Get as string (allocates)
html := b.String()

// Get as bytes (better for HTTP responses)
w.Write(b.Bytes())

// Reset for reuse
b.Reset()

---

Common Patterns

Conditional Elements

// Using Wrap
b.Div().R(
    b.Wrap(func() {
        if showHeader {
            b.H1().T("Header")
        }
    }),
    b.P().T("Always shown"),
)

// Using component conditional
func renderOptional(b *element.Builder, show bool, content string) any {
    if show {
        b.P().T(content)
    }
    return nil
}

Building Tables

b.Table().R(
    b.THead().R(
        b.Tr().R(
            b.Th().T("Name"),
            b.Th().T("Value"),
        ),
    ),
    b.TBody().R(
        element.ForEach(data, func(row DataRow) {
            b.Tr().R(
                b.Td().T(row.Name),
                b.Td().T(row.Value),
            )
        }),
    ),
)

Form Elements

b.Form("method", "post", "action", "/submit").R(
    b.Label("for", "email").T("Email:"),
    b.Input("type", "email", "id", "email", "name", "email"),
    b.Br(),
    b.Label("for", "password").T("Password:"),
    b.Input("type", "password", "id", "password", "name", "password"),
    b.Br(),
    b.ButtonClass("btn", "type", "submit").T("Submit"),
)

---

Best Practices

1. Always use Builder - Never create Elements directly
2. Terminate all elements - Use R(), T(), or F() on every non-self-closing element
3. Use Class methods - DivClass() is cleaner than Div("class", ...)
4. Prefer T() for text-only - More efficient than R(b.T(...))
5. Use pooling in handlers - AcquireBuilder()/ReleaseBuilder() for HTTP
6. Use Bytes() for responses - Avoids string allocation
7. Create components - For reusable UI patterns
8. Enable debug mode - During development to catch issues early

---

Quick Reference

Task	Code
Create builder	b := element.B()
Pooled builder	b := element.AcquireBuilder()
Element with children	b.Div().R(children...)
Element with text	b.P().T("text")
Formatted text	b.P().F("Count: %d", n)
Add class	b.DivClass("name")
Attributes	b.A("href", "/", "class", "link")
Iterate slice	element.ForEach(items, func(i T) { ... })
Render component	comp.Render(b)
Multiple components	element.RenderComponents(b, c1, c2)
Get output	b.String() or b.Bytes()