1.假如有如下for循环

for(
let i = (setTimeout(() => console.log(i),2333),0);
i < 2;
i++
){
}

请问在2333毫秒之后输出几？

2.for...in 佯谬

https://wdd.js.org/i-realy-dont-know-js.html

var scores = [10,11,12];
var total = 0;

for(var score in scores){
  total += score;
}

var mean = total/scores.length;
console.log(mean);

3.for in 潜规则

Array.prototype.contains = function(item) {
  return this.indexOf(item) >= 0
}

for(let key in [1,2,3,4]) {
  console.log(key)
}