Go Templates

A template is an HTML file with holes in it. You write the page once, mark where the data goes, and your handler supplies the values — so one file serves every user, every post, every search result.

Lemmego uses Go’s own html/template for this, so there is no new language to learn, and it adds two things on top: your templates are read once and kept in memory rather than re-read per request, and it works out which file is a page and which is a wrapper from the filename.

That last part is worth knowing first, because it is why the naming matters.

Template conventions

Three kinds of file, told apart by their suffix:

Suffix	Purpose	Example
`*.page.gohtml`	Page template (full page)	`index.page.gohtml`
`*.layout.gohtml`	Layout template (wraps page)	`base.layout.gohtml`
`*.partial.gohtml`	Partial/snippet	`header.partial.gohtml`

The template engine automatically discovers layouts and partials by walking up the directory tree from the page’s location.

Rendering a Template

import "github.com/lemmego/api/res"

func MyHandler(c app.Context) error {
    tmpl := res.NewTemplate(c, "index.page.gohtml")
    tmpl = tmpl.WithData(map[string]any{
        "title": "Welcome",
        "users": users,
    })
    return c.Render(tmpl)
}

Template with Data

tmpl := res.NewTemplate(c, "index.page.gohtml")
tmpl = tmpl.
    WithData(map[string]any{
        "title": "Users",
        "items": items,
    }).
    WithIntMap(map[string]int{
        "count": total,
    }).
    WithBoolMap(map[string]bool{
        "isAdmin": isAdmin,
    }).
    WithValidationErrors(errs)

Custom Functions

tmpl := res.NewTemplate(c, "index.page.gohtml")
tmpl = tmpl.WithFuncMap(template.FuncMap{
    "formatDate": func(t time.Time) string {
        return t.Format("January 2, 2006")
    },
})

Layout Templates

Layout templates wrap page content. The engine discovers *.layout.gohtml files in parent directories:

<!-- templates/base.layout.gohtml -->
<!DOCTYPE html>
<html>
<head>
    <title>{{block "title" .}}My App{{end}}</title>
</head>
<body>
    <nav>{{block "nav" .}}{{end}}</nav>
    <main>{{block "content" .}}{{end}}</main>
</body>
</html>

<!-- templates/index.page.gohtml -->
{{define "title"}}Home{{end}}
{{define "content"}}
    <h1>Welcome {{.title}}</h1>
{{end}}

Partial Templates

Partials are reusable snippets, discovered automatically from parent directories:

<!-- templates/header.partial.gohtml -->
<header>
    <h1>{{.appName}}</h1>
</header>

Template Cache

Templates are parsed and cached at application startup in init():

func init() {
    createTemplateCache()
}

The cache walks the templates/ directory, parses all *.page.gohtml files, and discovers their layouts and partials. This means template parsing errors are caught at startup, not at request time.

Error Pages

The generated project includes error pages for common HTTP status codes:

401.page.gohtml — Unauthorized
403.page.gohtml — Forbidden
404.page.gohtml — Not Found
419.page.gohtml — Page Expired (CSRF)
500.page.gohtml — Internal Server Error

Frontend Templ