SOURCE

// let arr = [
//     {id: 1, name: '部门1', pid: 0},
//     {id: 2, name: '部门2', pid: 1},
//     {id: 3, name: '部门3', pid: 1},
//     {id: 4, name: '部门4', pid: 3},
//     {id: 5, name: '部门5', pid: 4},
// ]
function arrToTree(arr) {
    let result = []
    let first = arr[0]
    arr.shift()
    if(arr instanceof Array && arr.length) {
        let f = arr.filter(d => d.pid === first.id)
        first.children = []
        if(f.length) {
            f.map(fd => {
                fd.children = []
                first.children.push(fd)
            })
            arr = arr.filter(d => d.pid !== first.id)
            let temp = arrToTree(arr)
            f.map((d,i) =>{
                if(temp.length && d.id === temp[0].pid) {
                    f[i].children = temp
                }
            })
            result.push(first)
        } else {
            first.children = arrToTree(arr)
        }
    }
    return result
}
function test(){
    let random = randomArr()
    let _t1 = performance.now();
    let tree = arrToTree(random)
    let _t2 = performance.now();
    console.log(_t2 - _t1);
}
function randomArr() {
    let arr = []
    for(let i=0; i< 1000; i++) {
        let randNum1 = Math.floor(Math.random() * 10)
        let randNum2 = Math.floor(Math.random() * 10)
        let randNum3 = Math.floor(Math.random() * 10)
        arr.push({
            id: randNum1,
            name: '部门'+randNum2,
            pid: randNum3,
        })
    }
    return arr
}
test()