function compare(times) {
  let a = { key: {} };
  let temp = a;
  for (let i = 0; i < times; i++) {
    let tmp = temp['key'];
    tmp['key'] = {};
    temp = tmp;
  }
  temp['key']['key'] = 'surprise';

  let d0 = new Date();
  let i = a;
  while (i['key'] !== 'surprise') {
    i = i['key'];
  }
  console.log('[] time', new Date() - d0);

  let d1 = new Date();
  let ii = a;
  while (ii.key !== 'surprise') {
    ii = ii.key;
  }
  console.log('. time', new Date() - d1);
}

var list = ['a', 'b', 'c', 'd'];
/*
//这一节为了验证对象复杂度对其的影响..
//实际上由于Object是类似hash表的结构
//所以实际上注释或者放开对这道题的结论并不影响，只是最后的总耗时线性增加而已
[...Array(100).keys()].forEach(num=>{
    list.push(num);
})
*/
var testObj = {};

list.forEach(key => {
    testObj[key] = {};
    list.forEach(key1 => {
        testObj[key][key1] = {};
        list.forEach(key2 => {
            testObj[key][key1][key2] = {};
            list.forEach(key3 => {
                testObj[key][key1][key2][key3] = Math.floor(Math.random() * 10);
            })
        })
    })
})

function testTypeA(num){
    console.time(`a.b.c.d :${num}`);
    for(var i =0;i<num;i++){
        var value = testObj.a.b.c.d;
    }
    console.timeEnd(`a.b.c.d :${num}`);
}

function testTypeB(num){
    console.time(`['a']['b']['c']['d'] :${num}`);
    for(var i =0;i<num;i++){
        var value = testObj['a']['b']['c']['d'];
    }
    console.timeEnd(`['a']['b']['c']['d'] :${num}`);
}
//测试组，每组测5次
var testList = ['10000000','15000000','20000000','30000000']
testList.forEach(num=>{
    [...Array(5).keys()].forEach(()=>{
        testTypeA(num);
        testTypeB(num);
    })
})