When i call this function
getQuestions = () => {
this.setState({ loading: true })
const { data } = this.props
axios
.get(data.questions)
.then((res) => {
this.setState({
loading: false,
questions: res.data,
})
this.initialQuestions = res.data
})
.catch((err) =>
this.setState({
loading: false,
questions: [],
})
)
}
it updates the array questions in state and array initialQuestions variable in constructor. The state questions represents the values form inputs. The inputs are handled in child component with this code
onChange = (e) => {
const { hasChanged, setQuestions } = this.props
// Update questions
let questions = this.props.questions
questions[e.target.getAttribute('data-id')][e.target.name] =
e.target.value
setQuestions(questions)
}
setQuestions is passed in props as setQuestions={(state) => this.setState({ questions: state })}
So when i change the value of inputs the onChange function is called and it changes the parent component questions in state. But the parent variable this.initialQuestions also is being changed to the questions value from state, but I don’t know why
Edit:
That’s the code you should be able to run
const { Component } = React;
const Textarea = "textarea";
const objectsEquals = (obj1, obj2) =>
Object.keys(obj1).length === Object.keys(obj2).length &&
Object.keys(obj1).every((p) => obj1[p] === obj2[p])
class QuestionList extends React.Component {
static propTypes = {
questions: PropTypes.array,
removeQuestion: PropTypes.func.isRequired,
hasChanged: PropTypes.func.isRequired,
setQuestions: PropTypes.func.isRequired,
}
constructor(props) {
super(props)
this.questions = props.questions
this.onChange = this.onChange.bind(this)
}
onChange = (e) => {
const { hasChanged, setQuestions } = this.props
// Update questions
let questions = this.props.questions
questions[e.target.getAttribute('data-id')][e.target.name] =
e.target.value
setQuestions(questions)
if (hasChanged && this.questions.length > 0) {
// array of booleans, true if object has change otherwise false
const hasChangedArray = this.props.questions.map(
(_, index) =>
!objectsEquals(
this.questions[index],
this.props.questions[index]
)
)
console.log("hasChangedArray = ", hasChangedArray)
console.log("this.questions[0] = ", this.questions[0])
console.log("this.props.questions[0] = ", this.props.questions[0])
// If true in array than the form has changed
hasChanged(
hasChangedArray.some((hasChanged) => hasChanged === true)
)
}
}
render() {
const { removeQuestion, questions } = this.props
const questionList = questions.map((question, index) => (
<div className="card" key={index}>
<div className="card__body">
<div className="row">
<div className="col-sm-7">
<div className="form-control">
<label className="form-control__label">
Question:
</label>
<input
type="text"
id={`question-${index}`}
data-id={index}
onChange={this.onChange}
name="question"
value={
this.props.questions[index].question
}
className="form-control__input form control__textarea"
placeholder="Pass the question..."
rows="3"
/>
</div>
<div className="form-control">
<label className="form-control__label">
Summery:
</label>
<Textarea
id={`summery-${index}`}
data-id={index}
onChange={this.onChange}
name="summery"
value={this.props.questions[index].summery}
className="form-control__input form-control__textarea"
placeholder="Pass the summery..."
rows="3"
/>
</div>
</div>
</div>
</div>
</div>
))
return questionList
}
}
class Questions extends React.Component {
constructor(props) {
super(props)
this.initialQuestions = []
this.state = {
loading: true,
questions: [],
hasChanged: false,
}
this.getQuestions = this.getQuestions.bind(this)
this.resetForm = this.resetForm.bind(this)
}
resetForm = () => {
console.log("this.initialQuestions =", this.initialQuestions)
this.setState({
questions: this.initialQuestions,
hasChanged: false,
})
}
getQuestions = () => {
this.setState({ loading: true })
const { data } = this.props
// axios
// .get(data.questions)
// .then((res) => {
// this.setState({
// loading: false,
// questions: res.data,
// })
// this.initialQuestions = res.data
// })
// .catch((err) =>
// this.setState({
// loading: false,
// questions: [],
// })
// )
// You can't do a database request so here is some example code
this.setState({
loading: false,
questions: [
{
question: 'example-question',
summery: 'example-summery',
},
{
question: 'example-question-2',
summery: 'example-summery-2',
},
],
})
this.initialQuestions = [
{
question: 'example-question',
summery: 'example-summery',
},
{
question: 'example-question-2',
summery: 'example-summery-2',
},
]
}
componentDidMount = () => this.getQuestions()
render() {
const { loading, questions, hasChanged } = this.state
if (loading) return <h1>Loading...</h1>
return (
<form>
<QuestionList
questions={questions}
hasChanged={(state) =>
this.setState({ hasChanged: state })
}
setQuestions={(state) =>
this.setState({ questions: state })
}
/>
<button
type="reset"
onClick={this.resetForm}
className={`btn ${
!hasChanged
? 'btn__disabled'
: ''
}`}
>
Cancel
</button>
<button
type="submit"
className={`btn btn__contrast ${
!hasChanged
? 'btn__disabled'
: ''
}`}
>
Save
</button>
</form>
)
}
}
ReactDOM.render(<Questions />, document.querySelector("#root"));<script src="https://unpkg.com/react@17/umd/react.production.min.js"></script> <script src="https://unpkg.com/react-dom@17/umd/react-dom.production.min.js"></script> <script src="https://unpkg.com/prop-types@15/prop-types.min.js"></script> <div id="root"></div>
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Answer
Both state questions and class variable initialQuestions hold reference of res.data. Now when you update questions in onChange method, you are updating it by reference i.e directly mutating it and hence the class variable is also updated
You must not update it by reference but clone and update like below
onChange = (e) => {
const { hasChanged, setQuestions } = this.props
// Update questions
let questions = this.props.questions
questions = questions.map((question, idx) => {
if(idx === e.target.getAttribute('data-id')) {
return {
...question,
[e.target.name]: e.target.value
}
}
return question;
});
setQuestions(questions)
}