Is it fair to ask tricky questions during the interview? Let me know your opinion. Ready for a new challenge? Try to answer 7 Interview Questions on 'this' keyword. If you have had difficulties to answer some while reading the post, it's a good indicator of what you must study next! Still, they could be asked.Īnyways, many of these questions can truly assess if you are seasoned in JavaScript, like the tricky closure. I have the same feeling, especially regarding the eagle eye test. You can think that some of the questions are useless for interviewing. const variables are in a temporal dead zone until the declaration line const m圜onst = 3.14.įollow the guide JavaScript Variables Hoisting in Details to get a good grasp on hoisting. However, accessing m圜onst before the declaration line throws a ReferenceError. A hoisted var variable, before its initialization, has an undefined value. Hoisting and temporal dead zone are 2 important concepts that influence the lifecycle of JavaScript variables.Īccessing myVar before declaration evaluates to undefined. If you struggle understanding closures, I recommend reading A Simple Explanation of JavaScript Closures.ĭo you know how to fix the snippet to log 0, 1, and 2? Please write your solution in a comment below! 6. It is also one of the most reliable ways for an employer to filter out unsuitable candidates for a job post. It gives insights about the skillset, knowledge, and the ability of an individual to take on challenging tasks. An interview is an important part of the hiring process. That's why the output to the console is 3, 3 and 3. 20 Common JavaScript Interview Questions Updated on by Juan Cruz Martinez. log() reads the current value of variable i, which is 3, and logs to console 3.

The 3 scheduled log() callbacks are called by setTimeout().

It's important to understand that the closure captures i variable lexically. Log() is a closure that captures the variable i, which is defined in the outside scope of for() cycle.

When for() cycle completes, i variable has value 3.

Then setTimout() schedules an execution of log(). During each iteration a new function log() is created, which captures the variable i. There are 2 phases behind executing this snippet. When I first tried to solve it, this was my answer too! If you haven't heard about this tricky question before, most likely your answer is 0, 1 and 2: which is incorrect.

Javascript interview questions