I'm getting this error Uncaught TypeError: Cannot read property 'state' of undefined whenever I type anything in the input box of AuthorForm. I'm using React with ES7.
The error occurs on 3rd line of setAuthorState function in ManageAuthorPage. Regardless of that line of code even if I put a console.log(this.state.author) in setAuthorState, it will stop at the console.log and call out the error.
Can't find similar issue for someone else over the internet.
Here is the ManageAuthorPage code:
import React, { Component } from 'react';
import AuthorForm from './authorForm';
class ManageAuthorPage extends Component {
state = {
author: { id: '', firstName: '', lastName: '' }
};
setAuthorState(event) {
let field = event.target.name;
let value = event.target.value;
this.state.author[field] = value;
return this.setState({author: this.state.author});
};
render() {
return (
<AuthorForm
author={this.state.author}
onChange={this.setAuthorState}
/>
);
}
}
export default ManageAuthorPage
And here is the AuthorForm code:
import React, { Component } from 'react';
class AuthorForm extends Component {
render() {
return (
<form>
<h1>Manage Author</h1>
<label htmlFor="firstName">First Name</label>
<input type="text"
name="firstName"
className="form-control"
placeholder="First Name"
ref="firstName"
onChange={this.props.onChange}
value={this.props.author.firstName}
/>
<br />
<label htmlFor="lastName">Last Name</label>
<input type="text"
name="lastName"
className="form-control"
placeholder="Last Name"
ref="lastName"
onChange={this.props.onChange}
value={this.props.author.lastName}
/>
<input type="submit" value="Save" className="btn btn-default" />
</form>
);
}
}
export default AuthorForm
This question is related to
javascript
reactjs
ecmascript-6
ecmascript-7
react-state
Make sure you're calling super() as the first thing in your constructor.
You should set this for setAuthorState method
class ManageAuthorPage extends Component {
state = {
author: { id: '', firstName: '', lastName: '' }
};
constructor(props) {
super(props);
this.handleAuthorChange = this.handleAuthorChange.bind(this);
}
handleAuthorChange(event) {
let {name: fieldName, value} = event.target;
this.setState({
[fieldName]: value
});
};
render() {
return (
<AuthorForm
author={this.state.author}
onChange={this.handleAuthorChange}
/>
);
}
}
Another alternative based on arrow function:
class ManageAuthorPage extends Component {
state = {
author: { id: '', firstName: '', lastName: '' }
};
handleAuthorChange = (event) => {
const {name: fieldName, value} = event.target;
this.setState({
[fieldName]: value
});
};
render() {
return (
<AuthorForm
author={this.state.author}
onChange={this.handleAuthorChange}
/>
);
}
}
You have to bind your event handlers to correct context (this):
onChange={this.setAuthorState.bind(this)}
Source: Stackoverflow.com