手写-将虚拟 Dom 转化为真实 Dom

 let vdom = {
      tag: 'DIV',
      attrs: {
        id: 'app'
      },
      children: [
        {
          tag: 'SPAN',
          children: [
            { tag: 'A', children: 'hellow a' },
            { tag: 'A', children: [] }

          ]
        },
        {
          tag: 'SPAN',
          children: [
            { tag: 'A', children: [] },
            { tag: 'A', children: [] }
          ]
        }
      ]
    };

let _render = (vnode) => {
      if (typeof vnode === "number") {
        vnode = String(vnode);
      }
      if (typeof vnode === 'string') {
        return document.createTextNode(vnode);
      }
      if (vnode.tag) {
        let dom = document.createElement(vnode.tag);
        if (vnode.attrs) {
          Object.keys(vnode.attrs).map(key => {
            let value = vnode.attrs[key];
            dom.setAttribute(key, value);
          })
        }
        if (typeof vnode.children === 'string') {
            dom.innerHTML = vnode.children;
          }

        if (Array.isArray(vnode.children)) {
          vnode.children.forEach(child => {
            dom.appendChild(_render(child));
          });
        }
        return dom;
      }
    }