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20-dynamic-forms.html
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20-dynamic-forms.html
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<body>
<div id="root"></div>
<script src="https://unpkg.com/react@16.12.0/umd/react.development.js"></script>
<script src="https://unpkg.com/react-dom@16.12.0/umd/react-dom.development.js"></script>
<script src="https://unpkg.com/@babel/standalone@7.8.3/babel.js"></script>
<script type="text/babel">
function UsernameForm() {
const [username, setUsername] = React.useState('')
const isLowerCase = username === username.toLowerCase()
const error = isLowerCase ? null : 'Username must be lower case'
function handleSubmit(event) {
event.preventDefault()
alert(`You entered: ${username}`)
}
function handleChange(event) {
setUsername(event.target.value)
}
return (
<form onSubmit={handleSubmit}>
<div>
<label htmlFor="usernameInput">Username:</label>
<input id="usernameInput" type="text" onChange={handleChange} />
</div>
<div style={{color: 'red'}}>{error}</div>
<button disabled={Boolean(error)} type="submit">
Submit
</button>
</form>
)
}
ReactDOM.render(<UsernameForm />, document.getElementById('root'))
</script>
</body>