React: Unexpected warning when I use getDerivedStateFromProps

[rcwestlake]

Do you want to request a feature or report a bug?
Bug

What is the current behavior?

In v. 16.3.1, when I use the getDerivedStateFromProps method and I have a controlled component where the value of input field is this.state.{thefieldname}, I get a warning/error that says I am switching from controlled to uncontrolled or vice versa. If I remove the getDerivedStateFromProps, the error goes away.

If the current behavior is a bug, please provide the steps to reproduce and if possible a minimal demo of the problem. Your bug will get fixed much faster if we can run your code and it doesn't have dependencies other than React. Paste the link to your JSFiddle (https://jsfiddle.net/Luktwrdm/) or CodeSandbox (https://codesandbox.io/s/new) example below:

```import React, { Component } from 'react'

class UserSettings extends Component {
constructor(props) {
super(props)

this.state = {
  firstName: '',
  lastName: '',
  email: ''
}
this.handleChange = this.handleChange.bind(this)

}

handleChange(e) {
this.setState({
[e.target.name]: e.target.value
})
}

handleUpdateUser(e) {
e.preventDefault()
const { updateUser, uid } = this.props
updateUser(uid, this.state)
}

static getDerivedStateFromProps(nextProps) {
return {
firstName: nextProps.user.firstName,
lastName: nextProps.user.lastName,
email: nextProps.user.email
}
}

render() {
const { firstName, lastName, email } = this.state
return (

Settings

{this.props.user.authStatus}

First Name

type="text"
className="form-control"
name="firstName"
placeholder="First name"
value={firstName}
onChange={this.handleChange}
/>

Last Name

type="text"
className="form-control"
name="lastName"
placeholder="Last name"
value={lastName}
onChange={this.handleChange}
/>

Email

type="text"
className="form-control"
name="email"
placeholder="Email"
value={email}
onChange={this.handleChange}
/>

className="btn btn-primary"
onClick={this.handleUpdateUser}>
Update User Info

)
}
}

export default UserSettings
```

What is the expected behavior?
I don't expect to get that warning.

Which versions of React, and which browser / OS are affected by this issue? Did this work in previous versions of React?

React: 16.3.1
OS: Mac osSierra 10.12.6
Browser: Chrome

[gaearon]

Can you provide a complete example I could run please? On CodeSandbox or JSFiddle. The issue template includes links to those services.

[DemianD]

When the nextProps in getDerivedStateFromProps contain values like undefined or null for firstName, lastName or email, the component input will act as an "uncontrolled input".

This switch from a "controlled" input to an "uncontrolled input" will throw the warning.

https://jsfiddle.net/w1ys9g2j/

[TrySound]

@DemianD It's not related to getDerivedStateFromProps. <input /> should accept only string. Just don't pass undefined and null to the component.

[DemianD]

@TrySound I assumed that the getDerivedStateFromProps in his example, sets some values of the user-object in state to null or undefined, which will render an <input /> with value null or undefined.

One solution can be:

<input value={lastName || ''} />

[TrySound]

@DemianD Yep.

[rcwestlake]

thanks @TrySound and @DemianD