SOURCE

let tree = [
    {
      id: '1',
      title: '节点1',
      children: [
        {
          id: '1-1',
          title: '节点1-1'
        },
        {
          id: '1-2',
          title: '节点1-2'
        }
      ]
    },
    {
      id: '2',
      title: '节点2',
      children: [
        {
          id: '2-1',
          title: '节点2-1'
        }
      ]
    }
  ]


function treeForeach(tree,func){
  let node,list = [...tree]
  while(node = list.shift()){
    func(node)
    node.children && list.push(...node.children)
  }
}

treeForeach(tree,node => console.log(node.title))
// console.log(tree);