Question

When declaring a variable or constant, which keyword can lead to hard-to-find bugs due to undefined initialization during hoisting?

a) let
b) var
c) const
d) undefined

Answer 1

The keyword that can lead to bugs due to undefined initialization during hoisting is 'var'. It is hoisted to the top of its scope and initialized as undefined, which can cause unpredictable behavior in the code.

Step-by-step explanation:

When dealing with hoisting in JavaScript, the keyword that can lead to hard-to-find bugs due to undefined initialization is var. Unlike let or const, a variable declared with var is hoisted and initialized to undefined at the top of its scope, no matter where it has been declared within the function or globally. This can easily cause bugs because the code appears to reference the variable before it's actually declared, leading to unexpected behavior.

For example:

function example() {
console.log(myVar); // undefined, but no ReferenceError
var myVar = 'value';
}

This function prints undefined due to hoisting. However, if it used let instead of var:

function example() {
console.log(myVar); // ReferenceError: myVar is not defined
let myVar = 'value';
}

In this case, a ReferenceError is thrown because let does not hoist to the entire scope like var does.