Guess the Output JavaScript Challenge | Variable Scope, Hoisting & ReferenceError | Learn JavaScript

Can you guess the output in this JavaScript challenge question? This is one of common JavaScript interview questions. It's a trick javascript question. If you know enough about variable scope, function scope, hoisting, variable declaration and variable assignment in JavaScript, then this question should be easy for you.

The code results in a reference error because the let keyword is used to declare the variable num
within the arrow function. This creates a new variable with the same name as the existing global variable, and the global variable is not accessible within the function's scope.

JavaScript's variable hoisting mechanism moves the variable declaration to the top of the function,
but the assignment remains in its original place. When the function is executed, this console log is trying to access the local variable num which has not been assigned yet, so it returns undefined and a ReferenceError is thrown.

A quick fix for this issue would be to either change the let keyword to var or to remove the let keyword entirely, so the global variable can be accessed.

So to avoid such reference error in javascript, make sure you keep these things in mind.

It can be a good javascript interview question or frontend interview question. You may not be required to solve it on paper or whiteboard but the interviewer may ask you to give an idea on how to approach this algorithm. If you have an understanding of how to solve this problem or approach this algorithm, you will be able to answer it and get your next job as a frontend developer or full-stack developer.

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