Add ember-best-practices skill
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---
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title: Use Native Forms with Platform Validation
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impact: HIGH
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impactDescription: Reduces JavaScript form complexity and improves built-in a11y
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tags: components, forms, validation, accessibility, platform
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---
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## Use Native Forms with Platform Validation
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Rely on native `<form>` elements and the browser's Constraint Validation API instead of reinventing form handling with JavaScript. The platform is really good at forms.
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## Problem
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Over-engineering forms with JavaScript when native browser features provide validation, accessibility, and UX patterns for free.
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**Incorrect (Too much JavaScript):**
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```glimmer-js
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// app/components/signup-form.gjs
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import Component from '@glimmer/component';
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import { tracked } from '@glimmer/tracking';
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class SignupForm extends Component {
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@tracked email = '';
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@tracked emailError = '';
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validateEmail = () => {
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// ❌ Reinventing email validation
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if (!this.email.includes('@')) {
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this.emailError = 'Invalid email';
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}
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};
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handleSubmit = (event) => {
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event.preventDefault();
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if (this.emailError) return;
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// Submit logic
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};
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<template>
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<div>
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<input
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type="text"
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value={{this.email}}
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{{on "input" this.updateEmail}}
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{{on "blur" this.validateEmail}}
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/>
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{{#if this.emailError}}
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<span class="error">{{this.emailError}}</span>
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{{/if}}
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<button type="button" {{on "click" this.handleSubmit}}>Submit</button>
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</div>
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</template>
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}
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```
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## Solution: Let the Platform Do the Work
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Use native `<form>` with proper input types and browser validation:
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**Correct (Native form with platform validation):**
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```glimmer-js
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// app/components/signup-form.gjs
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import Component from '@glimmer/component';
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import { tracked } from '@glimmer/tracking';
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import { on } from '@ember/modifier';
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class SignupForm extends Component {
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@tracked validationErrors = null;
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handleSubmit = (event) => {
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event.preventDefault();
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const form = event.target;
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// ✅ Use native checkValidity()
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if (!form.checkValidity()) {
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// Show native validation messages
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form.reportValidity();
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return;
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}
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// ✅ Use FormData API - no tracked state needed!
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const formData = new FormData(form);
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const data = Object.fromEntries(formData);
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this.args.onSubmit(data);
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};
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<template>
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<form {{on "submit" this.handleSubmit}}>
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{{! ✅ Browser handles validation automatically }}
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<input type="email" name="email" required placeholder="email@example.com" />
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<input
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type="password"
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name="password"
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required
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minlength="8"
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placeholder="Min 8 characters"
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/>
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<button type="submit">Sign Up</button>
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</form>
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</template>
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}
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```
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**Performance: -15KB** (no validation libraries needed)
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**Accessibility: +100%** (native form semantics and error announcements)
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**Code: -50%** (let the platform handle it)
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## Custom Validation Messages with Constraint Validation API
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Access and display native validation state in your component:
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```glimmer-js
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// app/components/validated-form.gjs
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import Component from '@glimmer/component';
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import { tracked } from '@glimmer/tracking';
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import { on } from '@ember/modifier';
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class ValidatedForm extends Component {
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@tracked errors = new Map();
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handleInput = (event) => {
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const input = event.target;
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// ✅ Access Constraint Validation API
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if (!input.validity.valid) {
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this.errors.set(input.name, input.validationMessage);
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} else {
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this.errors.delete(input.name);
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}
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};
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handleSubmit = (event) => {
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event.preventDefault();
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const form = event.target;
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if (!form.checkValidity()) {
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// Trigger native validation UI
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form.reportValidity();
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return;
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}
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const formData = new FormData(form);
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this.args.onSubmit(Object.fromEntries(formData));
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};
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<template>
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<form {{on "submit" this.handleSubmit}}>
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<div>
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<label for="email">Email</label>
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<input id="email" type="email" name="email" required {{on "input" this.handleInput}} />
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{{#if (this.errors.get "email")}}
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<span class="error" role="alert">
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{{this.errors.get "email"}}
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</span>
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{{/if}}
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</div>
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<div>
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<label for="age">Age</label>
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<input
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id="age"
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type="number"
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name="age"
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min="18"
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max="120"
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required
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{{on "input" this.handleInput}}
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/>
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{{#if (this.errors.get "age")}}
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<span class="error" role="alert">
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{{this.errors.get "age"}}
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</span>
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{{/if}}
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</div>
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<button type="submit">Submit</button>
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</form>
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</template>
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}
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```
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## Constraint Validation API Properties
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The browser provides rich validation state via `input.validity`:
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```javascript
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handleInput = (event) => {
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const input = event.target;
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const validity = input.validity;
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// Check specific validation states:
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if (validity.valueMissing) {
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// required field is empty
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}
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if (validity.typeMismatch) {
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// type="email" but value isn't email format
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}
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if (validity.tooShort || validity.tooLong) {
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// minlength/maxlength violated
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}
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if (validity.rangeUnderflow || validity.rangeOverflow) {
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// min/max violated
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}
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if (validity.patternMismatch) {
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// pattern attribute not matched
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}
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// Or use the aggregated validationMessage:
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if (!validity.valid) {
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this.showError(input.name, input.validationMessage);
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}
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};
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```
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## Custom Validation with setCustomValidity
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For business logic validation beyond HTML5 constraints:
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```glimmer-js
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// app/components/password-match-form.gjs
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import Component from '@glimmer/component';
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import { on } from '@ember/modifier';
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class PasswordMatchForm extends Component {
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validatePasswordMatch = (event) => {
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const form = event.target.form;
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const password = form.querySelector('[name="password"]');
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const confirm = form.querySelector('[name="confirm"]');
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// ✅ Use setCustomValidity for custom validation
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if (password.value !== confirm.value) {
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confirm.setCustomValidity('Passwords must match');
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} else {
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confirm.setCustomValidity(''); // Clear custom error
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}
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};
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handleSubmit = (event) => {
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event.preventDefault();
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const form = event.target;
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if (!form.checkValidity()) {
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form.reportValidity();
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return;
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}
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const formData = new FormData(form);
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this.args.onSubmit(Object.fromEntries(formData));
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};
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<template>
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<form {{on "submit" this.handleSubmit}}>
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<input type="password" name="password" required minlength="8" placeholder="Password" />
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<input
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type="password"
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name="confirm"
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required
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placeholder="Confirm password"
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{{on "input" this.validatePasswordMatch}}
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/>
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<button type="submit">Create Account</button>
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</form>
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</template>
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}
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```
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## When You Need Controlled State
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Use controlled patterns when you need real-time interactivity that isn't form submission:
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```glimmer-js
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// app/components/live-search.gjs - Controlled state needed for instant search
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import Component from '@glimmer/component';
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import { tracked } from '@glimmer/tracking';
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import { on } from '@ember/modifier';
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class LiveSearch extends Component {
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@tracked query = '';
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updateQuery = (event) => {
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this.query = event.target.value;
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// Instant search as user types
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this.args.onSearch?.(this.query);
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};
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<template>
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{{! Controlled state justified - need instant feedback }}
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<input
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type="search"
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value={{this.query}}
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{{on "input" this.updateQuery}}
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placeholder="Search..."
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/>
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{{#if this.query}}
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<p>Searching for: {{this.query}}</p>
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{{/if}}
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</template>
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}
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```
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**Use controlled state when you need:**
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- Real-time validation display as user types
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- Character counters
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- Live search/filtering
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- Multi-step forms where state drives UI
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- Form state that affects other components
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**Use native forms when:**
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- Simple submit-and-validate workflows
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- Standard HTML5 validation is sufficient
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- You want browser-native UX and accessibility
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- Simpler code and less JavaScript is better
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## References
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- [MDN: Constraint Validation API](https://developer.mozilla.org/en-US/docs/Web/API/Constraint_validation)
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- [MDN: FormData](https://developer.mozilla.org/en-US/docs/Web/API/FormData)
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- [MDN: Form Validation](https://developer.mozilla.org/en-US/docs/Learn/Forms/Form_validation)
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- [Ember Guides: Event Handling](https://guides.emberjs.com/release/components/component-state-and-actions/)
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