amplify getting started

lambda function
----
exports.handler = async (event) => {
    console.log(event)
    const customerId = event.pathParameters.customerId;
    const customer = {'customerId': customerId, 'customerName': "Customer " + customerId };
    const response = {
        statusCode: 200,
    //  Uncomment below to enable CORS requests
     headers: {
         "Access-Control-Allow-Origin": "*",
         "Access-Control-Allow-Headers": "*"
     }, 
        body: JSON.stringify(customer),
    };
    return response;
};

index.js
---
import React from 'react';
import ReactDOM from 'react-dom';
import './index.css';
import App from './App';
import reportWebVitals from './reportWebVitals';
import Amplify from "aws-amplify";
import awsExports from "./aws-exports";
Amplify.configure(awsExports);

ReactDOM.render(
  <React.StrictMode>
    <App />
  </React.StrictMode>,
  document.getElementById('root')
);

// If you want to start measuring performance in your app, pass a function
// to log results (for example: reportWebVitals(console.log))
// or send to an analytics endpoint. Learn more: https://bit.ly/CRA-vitals
reportWebVitals();


app.js
---
import logo from './logo.svg';
import './App.css';
import Amplify, { API } from 'aws-amplify'
import React, { useEffect, useState } from 'react'

const myAPI = "YOUR API HERE"
const path = '/customers'; 

const App = () => {
  const [input, setInput] = useState("")
  const [customers, setCustomers] = useState([])

  //Function to fetch from our backend and update customers array
  function getCustomer(e) {
    let customerId = e.input
    API.get(myAPI, path + "/" + customerId)
       .then(response => {
         console.log(response)
         let newCustomers = [...customers]
         newCustomers.push(response)
         setCustomers(newCustomers)

       })
       .catch(error => {
         console.log(error)
       })
  }

  return (
    
    <div className="App">
      <h1>Super Simple React App</h1>
      <div>
          <input placeholder="customer id" type="text" value={input} onChange={(e) => setInput(e.target.value)}/>      
      </div>
      <br/>
      <button onClick={() => getCustomer({input})}>Get Customer From Backend</button>

      <h2 style={{visibility: customers.length > 0 ? 'visible' : 'hidden' }}>Response</h2>
      {
       customers.map((thisCustomer, index) => {
         return (
        <div key={thisCustomer.customerId}>
          <span><b>CustomerId:</b> {thisCustomer.customerId} - <b>CustomerName</b>: {thisCustomer.customerName}</span>
        </div>)
       })
      }
    </div>
  )
}

export default App;

After some trial and error, I was able to get this working with the latest/current version of Amplify (Gen 2).

See AWS Amplify Dev Center - Set up Amplify REST API for the example I referenced.

Here are the changes I made to the author's original index.js and App.js:

index.js

Replace line 6:
import Amplify from "aws-amplify";
with a slightly modified version using curly braces:
import { Amplify } from "aws-amplify";

App.js

Replace the older style API import on line 3:
import Amplify, { API } from 'aws-amplify'
with the newer get() method:
import { get } from 'aws-amplify/api';

Replace the getCustomer() function on lines 14-27:

function getCustomer(e) {
    let customerId = e.input
    API.get(myAPI, path + "/" + customerId)
       .then(response => {
         console.log(response)
         let newCustomers = [...customers]
         newCustomers.push(response)
         setCustomers(newCustomers)

       })
       .catch(error => {
         console.log(error)
       })
  }

with a version that uses the new get() method:

  async function getCustomer(e) {
    let customerId = e.input
    const restOperation = get({apiName: myAPI, path: path + "/" + customerId})
    const { body } = await restOperation.response;
    const response = await body.json();
    console.log(response)
    let newCustomers = [...customers]
    newCustomers.push(response)
    setCustomers(newCustomers)
  }

Another thing that got me was using the wrong value for myAPI. I originally pulled the first part of the API URL and it threw the following error when I tried to click the button to submit a customerId:

API name is invalid.
InvalidApiName: API name is invalid.

I found the correct value in \amplify\#current-cloud-backend\backend-config.json under the "api" key (line 3 for me).

Also, I'm probably the only dummy that copied the code and somehow skipped that line of App.js. I was getting the following error until I realized what was going on:

export 'default' (imported as 'App') was not found in './App' (module has no exports)

Don't forget the last line of App.js:
export default App;

Hope this help!

@johnyarbi Super Super helpful.

Thank you!