Black box function

blackbox.js

function blackBox() {
  var input = [0, 1, 2, 3, 4];
  var results = [];
  for (var i = 0; i < input.length; i++) {
    results.push(
      new Promise(function(resolve) {
        setTimeout(function() {
          resolve(i);
        }, 200);
      })
    );
  }
  Promise.all(results).then(console.log);
}

component.jsx

import React, { Component } from "react";

class MyComponent extends Component {
  state = {
    valueLength: 0
  };

  componentDidMount() {
    this.setState({ valueLength: this.props.value.length });
  }

  componentDidUpdate() {
    this.setState({ valueLength: this.props.value.length });
  }

  render() {
    const { valueLength } = this.state;
    const { value } = this.props;
    return <p>{value} is {valueLength} chars long</p>;
  }
}