form

tinywasm/form

Fast form generation from Go structs for TinyGo + WASM. Uses fmt.Fielder interface for zero-reflection data binding. Input types are assigned via fmt.Widget in the schema (generated by ormc) — no magic name matching.

Rules (Non-Negotiable)

• No stdlib imports in library code. Never errors, strconv, strings, reflect.
• Use github.com/tinywasm/fmt: fmt.Err("Noun", "Adjective") for errors, fmt.Convert(s).Int() instead of strconv.Atoi, fmt.Contains(s, sub) instead of strings.Contains.
• No maps in inputs: Use slices. Maps increase WASM binary size.
• No reflect at runtime.

Quick Start

// User struct implements fmt.Fielder (generated by ormc).
// Each field in Schema() has a Widget assigned (e.g. input.NewEmail()).
f, err := form.New("parent-id", &User{Name: "John"})
html := f.RenderHTML()    // render to HTML string

How Field Matching Works

form.New() iterates data.Schema(). For each field:

1. If field.Widget == nil → field is skipped (no UI binding).
2. field.Widget.Clone(formID, fieldName) creates a positioned input instance.
3. The result is type-asserted to input.Input — if it fails, the field is skipped.
4. Constraint-based defaults are applied (e.g. NotNull → SetRequired(true)).
5. Current value from data.Pointers() is bound to the input.

There is no registry-based name matching. Each field's Widget is set explicitly in the schema by ormc.

Input Interface

// input.Input — defined in input/interface.go
type Input interface {
    fmt.Widget    // Type(), Validate(value string) error, Clone(parentID, name string) Widget
    dom.Component // GetID(), SetID(), RenderHTML(), Children()
}

Each concrete type (Email, Text, etc.) provides:

• NewXxx() fmt.Widget — template instance for use in schema (no position).
• Clone(parentID, name string) fmt.Widget — creates a positioned copy ready for rendering.
• Type() string — semantic input type name (e.g. "email").
• Validate(value string) error — validates input value via Permitted rules.

Public API

form.New(parentID string, data fmt.Fielder) (*Form, error)

Creates a Form from a Fielder. Uses data.Schema() to resolve inputs via field.Widget. Form id = parentID + "." + resolveStructName(data).

form.RegisterInput(inputs ...input.Input)

Registers custom input types globally. Used for explicit lookup via findInputByType(). Not called automatically — no init() auto-registration.

form.SetGlobalClass(classes ...string)

Sets CSS classes applied to all new forms.

Form Methods

Namer Interface

Fielder types can optionally implement Namer to customize the form name:

type Namer interface {
    FormName() string
}

If not implemented, defaults to "form".

WASM Event Flow

dom.Mount("root", f)
  -> f.RenderHTML() injected into DOM
  -> f.OnMount():
      el.On("input",  fn) -> SetValues + Validate per input
      el.On("change", fn) -> same (for select/radio/checkbox)
      el.On("submit", fn) -> PreventDefault -> SyncValues(f.data) -> Validate -> onSubmit(f.data)

One listener per form (not per input) = fewer closures = smaller WASM binary.

Standard Input Types

17 built-in types in input/:

Struct Tags

Tags are parsed at generation time by ormc and populate fmt.Field schema:

Runtime overrides: f.Input("Field").SetPlaceholder(), f.SetOptions("Field", ...).

Validation Engine (fmt.Permitted)

type Permitted struct {
	Letters    bool     // a-z, A-Z (and ñ/Ñ)
	Tilde      bool     // á, é, í, ó, ú
	Numbers    bool     // 0-9
	Spaces     bool     // ' '
	BreakLine  bool     // '\n'
	Tab        bool     // '\t'
	Extra      []rune   // additional allowed characters
	NotAllowed []string // disallowed substrings
	Minimum    int      // minimum length
	Maximum    int      // maximum length
}

File Map

Documentation Index

• API Reference — additional detail on Validate, SyncValues, Permitted
• Design & Architecture — core layers and philosophy
• Struct Tags — tag format and runtime overrides
• Standard Types — quick reference of 17 input types
• Implementation Notes — file map, adding new inputs, constraints
• Interactivity & Mounting — WASM event handling detail