[
{ id: 19, pid: 0, name: 'nodejs' },
{ id: 20, pid: 19, name: 'express' },
{ id: 21, pid: 19, name: 'mongodb' },
{ id: 60, pid: 20, name: 'ejs' },
{ id: 59, pid: 0, name: '前端開發(fā)' },
{ id: 70, pid: 59, name: 'javascript' },
{ id: 71, pid: 59, name: 'css' },
{ id: 72, pid: 59, name: 'html' },
{ id: 73, pid: 59, name: 'bootstrap' },
{ id: 61, pid: 0, name: '視覺設(shè)計' },
{ id: 63, pid: 61, name: '網(wǎng)頁設(shè)計' },
]

[
{ id: 19, pid: 0, name: 'nodejs',
 children:[
   { id: 20, pid: 19, name: 'express',children:[{ id: 60, pid: 20, name: 'ejs' }]},
   { id: 21, pid: 19, name: 'mongodb' }
   ]
},
{ id: 59, pid: 0, name: '前端開發(fā)',
 children:[
  { id: 70, pid: 59, name: 'javascript' },
  { id: 71, pid: 59, name: 'css' },
  { id: 72, pid: 59, name: 'html' },
  { id: 73, pid: 59, name: 'bootstrap' }
   ]
},
{ id: 61, pid: 0, name: '視覺設(shè)計',children:[{ id: 63, pid: 61, name: '網(wǎng)頁設(shè)計' }]},
]

//list 轉(zhuǎn)成樹形json
function listToTree(list,pid) {
var ret = [];//一個存放結(jié)果的臨時數(shù)組
for(var i in list) {
if(list[i].pid == pid) {//如果當(dāng)前項的父id等于要查找的父id，進(jìn)行遞歸
 list[i].children = listToTree(list, list[i].id);
 ret.push(list[i]);//把當(dāng)前項保存到臨時數(shù)組中
}
}
return ret;//遞歸結(jié)束后返回結(jié)果
}

var tree=listToTree(list,0);//調(diào)用函數(shù)，傳入要轉(zhuǎn)換的list數(shù)組，和樹中頂級元素的pid

console.log(tree);

//在網(wǎng)頁中添加下拉框容器
<select id="selectbox" name=""></select>
//js腳本，遞歸生成
//獲取容器對象
var selectbox=document.getElementById("selectbox");

//生成樹下拉菜單
var j="-";//前綴符號，用于顯示父子關(guān)系，這里可以使用其它符號
function creatSelectTree(d){
 var option="";
 for(var i=0;i<d.length;i++){
 if(d[i].children.length){//如果有子集
  option+="<option value='"+d[i].id+"'>"+j+d[i].name+"</option>";
 j+="-";//前綴符號加一個符號
  option+=creatSelectTree(d[i].children);//遞歸調(diào)用子集
 j=j.slice(0,j.length-1);//每次遞歸結(jié)束返回上級時，前綴符號需要減一個符號
  }else{//沒有子集直接顯示
  option+="<option value='"+d[i].id+"'>"+j+d[i].name+"</option>";
  }
  }
 return option;//返回最終html結(jié)果
 }

//調(diào)用函數(shù)，并將結(jié)構(gòu)出入到下拉框容器中
selectbox.innerHTML=creatSelectTree(tree);