React

HTML

<div id="app"></div>

CSS

body {
  background: #20262E;
  padding: 20px;
  font-family: Helvetica;
}

#app {
  background: #fff;
  border-radius: 4px;
  padding: 20px;
  transition: all 0.2s;
}

li {
  margin: 8px 0;
}

h2 {
  font-weight: bold;
  margin-bottom: 15px;
}

.done {
  color: rgba(0, 0, 0, 0.3);
  text-decoration: line-through;
}

input {
  margin-right: 5px;
}

React

const First = () => {
	const numbers = [1, 2, 3]
	return <div>
	  <Second nums = {numbers}/>
	</div>
}

const Second = ({ nums }) => {
	console.log(nums)
  return <div>
    Numbers: {nums.toString()}
  </div>
}

ReactDOM.render(<First />, document.querySelector("#app"))