Creación de formularios accesibles: más allá del HTML semántico

<!-- ❌ Implicit association only works visually -->
<div>
  Email
  <input type="email" />
</div>
 
<!-- ❌ Placeholder as label: disappears on focus -->
<input type="email" placeholder="Email address" />

<!-- ✅ Explicit label association -->
<div>
  <label for="user-email">Email address</label>
  <input
    type="email"
    id="user-email"
    name="email"
    autocomplete="email"
    required
    aria-describedby="email-hint"
  />
  <p id="email-hint" class="hint-text">
    We'll use this for account recovery only.
  </p>
</div>

<!-- ❌ Error message not associated with input -->
<label for="password">Password</label>
<input type="password" id="password" />
<span class="error" style="color: red;">
  Password must be at least 8 characters
</span>

<!-- ✅ Error properly associated and announced -->
<label for="password">Password</label>
<input
  type="password"
  id="password"
  aria-invalid="true"
  aria-describedby="password-error password-hint"
  aria-required="true"
/>
<p id="password-error" class="error" role="alert">
  Password must be at least 8 characters
</p>
<p id="password-hint" class="hint">
  Include uppercase, lowercase, and a number.
</p>

// React component with proper error handling
interface FormFieldProps {
  id: string;
  label: string;
  type: string;
  error?: string;
  hint?: string;
  required?: boolean;
  value: string;
  onChange: (value: string) => void;
}
 
function FormField({
  id,
  label,
  type,
  error,
  hint,
  required,
  value,
  onChange,
}: FormFieldProps) {
  const errorId = `${id}-error`;
  const hintId = `${id}-hint`;
 
  const describedBy = [
    error ? errorId : null,
    hint ? hintId : null,
  ]
    .filter(Boolean)
    .join(" ");
 
  return (
    <div className="form-field">
      <label htmlFor={id}>
        {label}
        {required && <span aria-hidden="true"> *</span>}
      </label>
      <input
        id={id}
        type={type}
        value={value}
        onChange={(e) => onChange(e.target.value)}
        aria-invalid={error ? "true" : undefined}
        aria-describedby={describedBy || undefined}
        aria-required={required}
      />
      {error && (
        <p id={errorId} className="error" role="alert">
          {error}
        </p>
      )}
      {hint && (
        <p id={hintId} className="hint">
          {hint}
        </p>
      )}
    </div>
  );
}

// ❌ No focus management: user doesn't know where to start
function handleSubmit(errors: Map<string, string>) {
  if (errors.size > 0) {
    // Errors shown visually, but no focus guidance
    setErrors(errors);
  }
}

// ✅ Focus the first error field and provide summary
function handleSubmitAccessible(
  errors: Map<string, string>,
  formRef: React.RefObject<HTMLFormElement | null>
) {
  if (errors.size === 0) return;
 
  // Update error state
  setErrors(errors);
 
  // Wait for DOM update, then focus error summary
  requestAnimationFrame(() => {
    const summary = formRef.current?.querySelector(
      "[data-error-summary]"
    ) as HTMLElement | null;
 
    if (summary) {
      summary.focus();
    } else {
      // Fallback: focus first invalid field
      const firstError = formRef.current?.querySelector(
        "[aria-invalid='true']"
      ) as HTMLElement | null;
      firstError?.focus();
    }
  });
}
 
// Error summary component
function ErrorSummary({ errors }: { errors: Map<string, string> }) {
  if (errors.size === 0) return null;
 
  return (
    <div
      data-error-summary
      role="alert"
      tabIndex={-1}
      className="error-summary"
    >
      <h2>There are {errors.size} errors in your submission</h2>
      <ul>
        {Array.from(errors.entries()).map(([fieldId, message]) => (
          <li key={fieldId}>
            <a href={`#${fieldId}`}>{message}</a>
          </li>
        ))}
      </ul>
    </div>
  );
}

function DynamicFieldList({
  fields,
  onAdd,
  onRemove,
}: {
  fields: string[];
  onAdd: () => void;
  onRemove: (index: number) => void;
}) {
  const [announcement, setAnnouncement] = useState("");
 
  function handleAdd() {
    onAdd();
    setAnnouncement(
      `Item ${fields.length + 1} added. ${fields.length + 1} items total.`
    );
  }
 
  function handleRemove(index: number) {
    onRemove(index);
    setAnnouncement(
      `Item ${index + 1} removed. ${fields.length - 1} items total.`
    );
 
    // Focus the previous field or the add button
    requestAnimationFrame(() => {
      const prevField = document.getElementById(
        `field-${Math.max(0, index - 1)}`
      );
      if (prevField) {
        prevField.focus();
      }
    });
  }
 
  return (
    <fieldset>
      <legend>Phone numbers</legend>
 
      {/* Screen-reader-only live region */}
      <div
        aria-live="polite"
        aria-atomic="true"
        className="sr-only"
      >
        {announcement}
      </div>
 
      {fields.map((field, index) => (
        <div key={index} className="dynamic-field">
          <label htmlFor={`field-${index}`}>
            Phone number {index + 1}
          </label>
          <input
            id={`field-${index}`}
            type="tel"
            defaultValue={field}
            autoComplete="tel"
          />
          <button
            type="button"
            onClick={() => handleRemove(index)}
            aria-label={`Remove phone number ${index + 1}`}
          >
            Remove
          </button>
        </div>
      ))}
 
      <button type="button" onClick={handleAdd}>
        Add phone number
      </button>
    </fieldset>
  );
}

interface Step {
  id: string;
  label: string;
  completed: boolean;
}
 
function StepIndicator({
  steps,
  currentStep,
}: {
  steps: Step[];
  currentStep: number;
}) {
  return (
    <nav aria-label="Form progress">
      <ol className="step-indicator">
        {steps.map((step, index) => (
          <li
            key={step.id}
            aria-current={index === currentStep ? "step" : undefined}
          >
            <span className="step-number" aria-hidden="true">
              {step.completed ? "✓" : index + 1}
            </span>
            <span className={index === currentStep ? "current" : ""}>
              {step.label}
              {step.completed && (
                <span className="sr-only"> (completed)</span>
              )}
              {index === currentStep && (
                <span className="sr-only"> (current step)</span>
              )}
            </span>
          </li>
        ))}
      </ol>
    </nav>
  );
}
 
function MultiStepForm({ steps }: { steps: Step[] }) {
  const [currentStep, setCurrentStep] = useState(0);
  const stepRef = useRef<HTMLDivElement>(null);
 
  function navigateToStep(newStep: number) {
    setCurrentStep(newStep);
 
    // Focus the step heading after navigation
    requestAnimationFrame(() => {
      const heading = stepRef.current?.querySelector("h2");
      heading?.focus();
    });
  }
 
  return (
    <form>
      <StepIndicator steps={steps} currentStep={currentStep} />
 
      <div ref={stepRef}>
        <h2 tabIndex={-1}>
          Step {currentStep + 1} of {steps.length}:{" "}
          {steps[currentStep].label}
        </h2>
 
        {/* Step content renders here */}
      </div>
 
      <div className="step-navigation">
        {currentStep > 0 && (
          <button
            type="button"
            onClick={() => navigateToStep(currentStep - 1)}
          >
            Back to {steps[currentStep - 1].label}
          </button>
        )}
        {currentStep < steps.length - 1 ? (
          <button
            type="button"
            onClick={() => navigateToStep(currentStep + 1)}
          >
            Continue to {steps[currentStep + 1].label}
          </button>
        ) : (
          <button type="submit">Submit form</button>
        )}
      </div>
    </form>
  );
}

// Automated testing with jest and testing-library
import { render, screen } from "@testing-library/react";
import userEvent from "@testing-library/user-event";
 
describe("FormField accessibility", () => {
  it("associates error message with input", () => {
    render(
      <FormField
        id="email"
        label="Email"
        type="email"
        error="Invalid email address"
        value=""
        onChange={() => {}}
      />
    );
 
    const input = screen.getByLabelText("Email");
    expect(input).toHaveAttribute("aria-invalid", "true");
    expect(input).toHaveAccessibleDescription("Invalid email address");
  });
 
  it("moves focus to error summary on submit", async () => {
    const user = userEvent.setup();
    render(<ContactForm />);
 
    await user.click(screen.getByRole("button", { name: /submit/i }));
 
    const summary = screen.getByRole("alert");
    expect(summary).toHaveFocus();
  });
 
  it("announces dynamic field additions", async () => {
    const user = userEvent.setup();
    render(<DynamicFieldList fields={["555-0100"]} onAdd={() => {}} onRemove={() => {}} />);
 
    await user.click(
      screen.getByRole("button", { name: /add phone/i })
    );
 
    expect(screen.getByText(/2 items total/i)).toBeInTheDocument();
  });
});