index.js

import React, { Component } from 'react';
import axios from 'axios';
import './App.css';

class App extends Component {
  constructor() {
    super();

    this.state = {
      images: [],
    };
  }

  onImageChange = event => {
    console.log(event.target.files);

    this.setState({
      images: event.target.files,
    });
  };

  onSubmit = e => {
    e.preventDefault();

    const formData = new FormData();

    Array.from(this.state.images).forEach(image => {
      formData.append('files', image);
    });

    axios
      .post(`http://localhost/api/<apiname>/upload`, formData, {
        headers: { 'Content-Type': 'multipart/form-data' },
      })
      .then(res => {
        console.log(res);
      })
      .catch(err => {
        console.log(err);
      });
  };

  render() {
    return (
      <div className="App">
        <form onSubmit={this.onSubmit}>
          <input
            type="file"
            name="files"
            onChange={this.onImageChange}
            alt="image"
          />
          <br />
          <button type="submit">Send</button>
        </form>
      </div>
    );
  }
}

export default App;