setTimeout + Closures Interview Question 🔥 | Namaste 🙏 JavaScript Ep. 11

TL;DR

Closures in JavaScript allow functions to remember and access variables from their lexical environment, even when executed in a different scope.

Transcript

now we will cover very important interview questions related to closures which is asked a lot of times in interviews and you know even very senior developers they pull their hairs right when they see like things are not working as expected and you know that is because we don't understand what happens behind the scenes so now let us see these exampl... Read More

Key Insights

• 🫥 The set timeout function in JavaScript does not wait for the timer to expire before executing the next line of code.
• 👻 Closures in JavaScript allow functions to retain access to variables from their lexical environment.
• 💌 The "let" keyword in a for loop can create a new copy of a variable for each iteration, solving issues with incorrect values in asynchronous operations.

Questions & Answers

Q: Why does the set timeout function not wait for the timer to expire in JavaScript?

JavaScript does not wait for anything and continues to execute the next line of code. The set timeout function attaches a timer to the callback function and stores it for later execution.

Q: What is a closure in JavaScript?

A closure is a function that retains access to variables from its lexical environment, even if executed in a different scope. It allows functions to "remember" and access these variables.

Q: How can closures help solve the problem of printing the wrong values in a loop?

By using the "let" keyword in the loop, a new copy of the variable is created for each iteration. This ensures that each set timeout function has its own unique reference to the variable.

Q: Why does using the "var" keyword in the loop result in printing the wrong values?

The "var" keyword does not create a new copy of the variable for each iteration. Instead, all set timeout functions refer to the same variable, which may have been modified by the time they execute.

Key Insights:

• The set timeout function in JavaScript does not wait for the timer to expire before executing the next line of code.
• Closures in JavaScript allow functions to retain access to variables from their lexical environment.
• The "let" keyword in a for loop can create a new copy of a variable for each iteration, solving issues with incorrect values in asynchronous operations.
• Understanding closures can help programmers avoid common interview challenges and better understand JavaScript's behavior.

Summary & Key Takeaways

• Closures are frequently asked interview questions and can be difficult to understand without proper knowledge.

• The set timeout function in JavaScript does not wait for the timer to expire before running the next line of code.

• Using the "let" keyword in a for loop can create a new copy of a variable for each iteration, solving the issue of printing the wrong values.