React的渲染element（做最少的DOM操作）

Rendering Elements

An element describes what you want to see on the screen.

原则：尽可能少的操作DOM

如下面react官网的例子就是很好的说明：

function tick() {
  const element = (
    <div>
      <h1>Hello, world!</h1>
      <h2>It is {new Date().toLocaleTimeString()}.</h2>
    </div>
  );
  ReactDOM.render(element, document.getElementById('root'));}

setInterval(tick, 1000);

Even though we create an element describing the whole UI tree on every tick, only the text node whose contents have changed gets updated by React DOM.

issues