Building Templ Components

Build type-safe HTML user interfaces in Go with the templ templating language. Templ compiles .templ files into Go code, providing compile-time type checking and excellent developer tooling.

Use this skill when creating templ components, working with templ syntax, integrating templ with HTTP servers, or setting up templ development workflows.

Quick Start

Installation

go install github.com/a-h/templ/cmd/templ@latest

Basic Component

Create a .templ file:

// hello.templ
package main

templ Hello(name string) {
    <div class="greeting">
        <h1>Hello, { name }!</h1>
    </div>
}

Generate Go code:

templ generate

Use in Go:

// main.go
package main

import (
    "net/http"
    "github.com/a-h/templ"
)

func main() {
    http.Handle("/", templ.Handler(Hello("World")))
    http.ListenAndServe(":8080", nil)
}

Core Concepts

Components

Components are Go functions returning templ.Component:

// Basic component
templ Greeting() {
    <p>Hello!</p>
}

// Component with parameters
templ UserCard(name string, age int) {
    <div class="card">
        <h2>{ name }</h2>
        <p>Age: { strconv.Itoa(age) }</p>
    </div>
}

// Exported component (uppercase)
templ Button(text string) {
    <button type="button">{ text }</button>
}

Expressions

Use { } for Go expressions:

templ Profile(user User) {
    <h1>{ user.Name }</h1>
    <p>{ fmt.Sprintf("Member since %d", user.Year) }</p>
}

Children

Wrap other components:

templ Layout(title string) {
    <!DOCTYPE html>
    <html>
        <head><title>{ title }</title></head>
        <body>
            { children... }
        </body>
    </html>
}

// Usage
@Layout("Home") {
    <main>Content here</main>
}

Conditional Rendering

templ Alert(show bool, message string) {
    if show {
        <div class="alert">{ message }</div>
    }
}

templ Status(level int) {
    if level > 80 {
        <span class="high">High</span>
    } else if level > 40 {
        <span class="medium">Medium</span>
    } else {
        <span class="low">Low</span>
    }
}

Loops

templ ItemList(items []string) {
    <ul>
        for _, item := range items {
            <li>{ item }</li>
        }
    </ul>
}

templ UserTable(users []User) {
    <table>
        for i, user := range users {
            <tr>
                <td>{ strconv.Itoa(i + 1) }</td>
                <td>{ user.Name }</td>
            </tr>
        }
    </table>
}

Component Composition

// Call other components with @
templ Page() {
    @Header()
    <main>
        @Sidebar()
        @Content()
    </main>
    @Footer()
}

// Pass components as parameters
templ Card(header templ.Component, body templ.Component) {
    <div class="card">
        <div class="card-header">@header</div>
        <div class="card-body">@body</div>
    </div>
}

CLI Commands

# Generate Go code from .templ files
templ generate

# Watch mode with live reload
templ generate --watch

# Format templ files
templ fmt .

# Start LSP server (for IDE support)
templ lsp

HTTP Integration

Using templ.Handler

// Simple handler
http.Handle("/", templ.Handler(HomePage()))

// With status code
http.Handle("/404", templ.Handler(NotFound(), templ.WithStatus(http.StatusNotFound)))

// With streaming
http.Handle("/stream", templ.Handler(LargePage(), templ.WithStreaming()))

Direct Render

func handler(w http.ResponseWriter, r *http.Request) {
    data := fetchData()
    component := DataPage(data)
    component.Render(r.Context(), w)
}

Reference Files

• Syntax details: See SYNTAX.md
• CSS styling: See CSS-STYLING.md
• JavaScript: See JAVASCRIPT.md
• CLI commands: See CLI.md
• HTTP integration: See HTTP.md
• Best practices: See PATTERNS.md

Common Patterns

Layout Pattern

templ Base(title string) {
    <!DOCTYPE html>
    <html lang="en">
        <head>
            <meta charset="UTF-8"/>
            <title>{ title }</title>
        </head>
        <body>
            { children... }
        </body>
    </html>
}

templ HomePage() {
    @Base("Home") {
        <h1>Welcome</h1>
    }
}

Form Pattern

templ LoginForm(errors map[string]string) {
    <form method="POST" action="/login">
        <label for="email">Email</label>
        <input type="email" id="email" name="email"/>
        if err, ok := errors["email"]; ok {
            <span class="error">{ err }</span>
        }

        <label for="password">Password</label>
        <input type="password" id="password" name="password"/>
        if err, ok := errors["password"]; ok {
            <span class="error">{ err }</span>
        }

        <button type="submit">Login</button>
    </form>
}

HTMX Integration

templ SearchButton() {
    <button
        hx-get="/search"
        hx-target="#results"
        hx-trigger="click"
    >
        Search
    </button>
    <div id="results"></div>
}