If you get this error "Uncaught TypeError: Cannot read properties of undefined (reading 'state')"
The reason for that kind of error is most likely that the state is in a method that is not bound to the component.
Here is how you can bind the method:
Option 1. Bind method in construction
constructor(props) {
super(props);
this.state = {
userName:"",
password:"",
};
this.handleSubmit = this.handleSubmit.bind(this);
}
...
handleSubmit (e) {
e.preventDefault();
if(this.state.password === "" && this.state.userName === "") {
alert("you cannot enter");
}
}
Option 2. Use fat arrow method
handleSubmit = (e) => {
e.preventDefault();
if(this.state.password === "" && this.state.userName === "") {
alert("you cannot enter");
}
}