Dare to challenge these 3 JavaScript questions

If you have dreams and dry goods, you can search for [Great Move to the World] on WeChat and pay attention to this Shawanzhi who is still washing dishes in the early hours of the morning.

This article GitHub https://github.com/qq449245884/xiaozhi has been included, there are complete test sites, materials and my series of articles for interviews with first-line manufacturers.

Recently, I changed jobs and participated in n interviews. The process is relatively pleasant experience. However, there are some very tricky issues, such as the following.

1. Unexpected global variable

 function crazyFunction() {
  var a = (b = 10);
}
crazyFunction();
console.log("b", typeof b === "undefined");
console.log("a", typeof a === "undefined");

2. Vision test

 const numbers = [1, 2, 3];
for (var index = 0; index < numbers.length; index++);{
  const number = numbers[index];
  console.log(number);
}

3. Tricky Closures

 let i;
for (i = 0; i < 3; i++) {
  const log = () => {
    console.log(i);
  };
  setTimeout(log, 100);
}

My questions 1 and 2 were all wrong, and I only answered question 3 correctly, and I cried. . .

You have the answer, now it will be revealed.

 1. b false
   a true
2. undefined
3. 3
   3
   3

The answer to my first question is

 b  true
a  false

On the contrary, a perfect miss.

My second answer is

 1
2
3

Have you found the problem, that's right

 for (var index = 0; index < numbers.length; index++); // 这里多了分号，真是考察眼力呀

If you have any ideas about the answer, you can leave a message and share, we will learn together.

The bugs that may exist in editing cannot be known in real time. In order to solve these bugs afterwards, a lot of time is spent on log debugging. By the way, here is a useful BUG monitoring tool , Fundebug .

comminicate

If you have dreams and dry goods, you can search for [Great Move to the World] on WeChat and pay attention to this Shawanzhi who is still washing dishes in the early hours of the morning.

This article GitHub https://github.com/qq449245884/xiaozhi has been included, there are complete test sites, materials and my series of articles for interviews with first-line manufacturers.