how to call data from backend in react code example

Example 1: fetch api react

// This is what I've been using, pretty straight forward
// It passes the JSON to the children as props
// Of course, you fetch what you will

import React, { Component, Fragment } from 'react';

export class FetchJsonController extends Component
{
	constructor(props) {
		super(props);
		this.state = {
			data: null,
		};
	}

	componentDidMount() {
		fetch(this.props.src)
			.then(response => response.json())
			.then(data => {
				console.log(data);
				this.setState({ data })
			});
	}

	render() {
		const _data = this.state.data;
		const children = React.Children.map(this.props.children, child => {
			return React.cloneElement(child, {
				jsonData: _data
			});
		});
		return (
			<div>{ children }</div>
		)
	}
}

// This is how it's used
// SomeCompnent will receive the JSON data
<FetchJsonController src="somefile.json">
  <SomeComponent />
</FetchJsonController>

Example 2: React get method

/* React get method.  */

componentWillMount(){
    fetch('/getcurrencylist',
    {
        /*
        headers: {
          'Content-Type': 'application/json',
          'Accept':'application/json'
        },
        */
        method: "get",
        dataType: 'json',
    })
    .then((res) => res.json())
    .then((data) => {
      var currencyList = [];
      for(var i=0; i< data.length; i++){
        var currency = data[i];
        currencyList.push(currency);
      }
      console.log(currencyList);
      this.setState({currencyList})
      console.log(this.state.currencyList);
    })
    .catch(err => console.log(err))
  }

Example 3: callback in react

import React, { useCallback } from 'react';

function MyComponent() {
  // handleClick is the same function object
  const handleClick = useCallback(() => {    console.log('Clicked!');  }, []);
  // ...
}

Example 4: how to connect react to backend

//put inside of package.json
"proxy": "http://localhost:8080"