What will the output be in the console for the statement console.log(x); let x = 10;?

What will the output be in the console for the statement console.log(x); let x = 10;?

• A. 10
• B. undefined
• C. ReferenceError
• D. NaN

Answer: (C)

When evaluating the statement `console.log(x); let x = 10;`, it's essential to understand JavaScript's hoisting behavior, particularly with `let` declarations. In JavaScript, variable declarations using `let` are hoisted to the top of their containing block; however, they are not initialized. Therefore, when the JavaScript engine encounters `let x = 10;`, it moves the declaration of `x` to the top of the block but does not assign it the value `10` yet. This results in a "temporal dead zone" until the line where `x` is actually initialized is executed. When `console.log(x);` is called, `x` is in this temporal dead zone, which means that accessing `x` at this point will throw a `ReferenceError` because `x` does not exist in the current scope yet. Thus, the output in the console will produce a `ReferenceError`, signifying that `x` is being referenced before it has been declared and initialized.

When evaluating the statement console.log(x); let x = 10;, it's essential to understand JavaScript's hoisting behavior, particularly with let declarations.

In JavaScript, variable declarations using let are hoisted to the top of their containing block; however, they are not initialized. Therefore, when the JavaScript engine encounters let x = 10;, it moves the declaration of x to the top of the block but does not assign it the value 10 yet. This results in a "temporal dead zone" until the line where x is actually initialized is executed.

When console.log(x); is called, x is in this temporal dead zone, which means that accessing x at this point will throw a ReferenceError because x does not exist in the current scope yet.

Thus, the output in the console will produce a ReferenceError, signifying that x is being referenced before it has been declared and initialized.