What happens when you log a var before declaration? Hoisting in Javascript? Asked in an Epam interview

Our Javascript Code:

console.log(x);
var x = "Hello";
console.log(x);

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Step-by-Step Explanation

🔸 Step 1: Hoisting in JavaScript

In JavaScript, variable declarations (var, function) are hoisted to the top of their scope during the compilation phase.

So the code:

console.log(x);
var x = "Hello";
console.log(x);

Is interpreted by JavaScript like this behind the scenes:

var x;            // Declaration is hoisted to the top
console.log(x);   // At this point, x exists but is `undefined`
x = "Hello";      // Now x is assigned the value "Hello"
console.log(x);   // So it logs "Hello"

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✔ Final Answer:

A) undefined Hello

This question appeared in the Epam 2nd round of interview, testing the candidate’s knowledge of hoisting with var variable in JavaScript.

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🚨 Common Mistake:

People often assume the first console.log(x) should throw a ReferenceError but it doesn't!

That would only happen if you used let or const:

console.log(x);
let x = "Hello"; // ❌ ReferenceError: Cannot access 'x' before initialization

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Remember Key Points:

• "var" declarations are hoisted, and initialize with undefined during memory creation phase of Execution Context. but let and const are not initialize with undefined.
• So before the assignment, the variable "var" exists with the value undefined. but the variable "let" and "const" give ReferenceError due to access before initialize any value.