How access specific DOM in React js - reactjs

Question

I'm trying to get input tags' HTML inner values when submitting a form.
private handleSubmit = (event: any) => {
event.preventDefault();
console.log(event.currentTarget);
};
When the submit the form, it calls the function handleSubmit and it console logs the following.
Under the form tag, the first div has username value and the second div has password value. I would like to acess the two values. I think I should use DOM to do that, but can't be sure if I'm going for the right direction cuz I found some postings saying using DOM is not recommended.
Can anyone explain how I can acheive this?

Answer 1

Ideally you should update your state as the user enters information, and then access the data from the state. This would also allow you to run any validation on the data prior to it going into the state if you'd like.
import React, { Component } from 'react';
import './App.css';
class App extends Component {
constructor(props) {
super(props);
this.state = {
username: null,
password: null
}
this.submitForm = this.submitForm.bind(this);
this.updateState = this.updateState.bind(this);
}
updateState (e) {
this.setState({[e.target.name]: e.target.value})
}
submitForm (e) {
e.preventDefault();
console.log(this.state);
}
render() {
return (
<div className="App">
<form onSubmit={this.submitForm}>
<input type="text" name="username" placeholder="username" onChange={this.updateState} /><br />
<input type="password" name="password" placeholder="password" onChange={this.updateState} /><br />
<button type="submit">Submit</button>
</form>
</div>
);
}
}
export default App;
The above code does the following:
Stores default values for username and password. While this isn't required, it makes the code more readable
binds this to functions that need to access state
Uses an updateState() function that is called onChange of the inputs
updateState uses the name attribute of the input as the key for the state
You could customize the updateState() function to do some validation, before saving to state if you'd like.
Excessive Rendering
ReactJS is pretty smart to no re-render the REAL DOM if your render() method doesn't actually rely on the state values that were updated; however, if you'd like to prevent ReactJS from even creating the Virtual DOM and comparing, you could utilize the shouldComponentUpdate() lifecycle hook.
In the particular example above, since render doesn't rely on ANYTHING in state, you could simply add the following method:
shouldComponentUpdate(prevState, nextState) {
return false;
}
That will prevent the render method from EVER re-rendering, which is most likely not going to work in a normal component, thus you could do something like this instead, only re-rendering on values you care about.
shouldComponentUpdate(prevState, nextState) {
if (nextState.email !== prevState.email) {
return true
}
return false;
}
Demo
https://repl.it/#AnonymousSB/SO53689072

Answer 2

If you want to use the DOM, once you have the form element (event.currentTarget in your case), you can use the .elements property to access a list of child inputs and buttons.
Alternatively, you can use React refs to keep track of the underlying HTML element when it's rendered.
render() {
return ... <input ref={(e) => this._name = e; } ....> ... ;
}
handleSubmit(e) {
var name = this._name ? this._name.value : '';
....
}

Answer 3

This can achieve what you want to
class Login extends Component{
state={
username:"",
password:""
}
onChange = (event)=>{
event.preventDefault()
this.setState({
[event.target.name]: event.target.value})
}
onSubmit = (event)=>{
event.preventDefault()
// submit whatever is in state from here
console.log(this.state)
}
render(){
return(<div>
<form onSubmit={handleSubmit}>
<input type="text" name="username" onChange={this.onChange} /><br />
<input type="password" name="password" onChange={this.onChange} /><br />
<button type="submit">Submit</button>
</form>
</div>)
}
}