什么是Virtual Dom
React和Vue2都使用了Virtual Dom技术，Virtual Dom并不是真正意义上的Dom，而是一个轻量级的JavaScript对象，在状态发生变化时，Virtual Dom会进行Diff运算，来更新只需要被替换的DOM，而不是全部重绘。
与DOM操作相比，Virtual Dom是基于JavaScript计算的，所以开销会小很多。
什么是render函数
Render函数通过Element的参数来创建Virtual Dom，结构精简，代码少且清晰，这里使用了一个demo实例来说明
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta http-equiv="X-UA-Compatible" content="ie=edge">
<title>Document</title>
<style>
div {
margin-left: 50px;
background-color: bisque;
}
</style>
</head>
<body>
<div>
</div>
<script>
const elementObj = {
tagName: 'div',
props: {'class': 'list'},
children: [
{tagName: 'div', props: {'class': 'list'}, content:"1",
children: [
{tagName: 'div', props: {'class': 'list'}, content:"一"},
{tagName: 'div', props: {'class': 'list'}, content:"二",
children: [
{tagName: 'div', props: {'class': 'list'}, content:"①"},
{tagName: 'div', props: {'class': 'list'}, content:"②"}
]
}
]},
{tagName: 'div', props: {'class': 'list'}, content:"2",
children: [
{tagName: 'div', props: {'class': 'list'}, content:"一"},
{tagName: 'div', props: {'class': 'list'}, content:"二"}
]
}
]
};
document.querySelector('div').appendChild(render(elementObj));
//深度遍历
function render (elementObj) {
//首先生成父元素
let el = document.createElement(elementObj.tagName);
for(propName in elementObj.props){
propValue = elementObj.props[propName];
el.setAttribute(propName, propValue);
}
if (elementObj.content) {
console.log(elementObj.content);
el.innerText = elementObj.content;
}
//如果children不为空
if (elementObj.children) {
elementObj.children.forEach(function(child){
el.appendChild(render(child));
}
);
}
return el;
}
</script>
</body>
</html>
