JavaScript : MCQs & PYQs with Explanation

Option C

In JavaScript, the + operator works as both addition and string concatenation. If any operand is a string, the operation becomes concatenation. In the given code, the expression is evaluated from left to right.
First, '4'+3 results in "43" because the number 3 is converted into a string. Then "43"+12.89 results in "4312.89", as the number is again converted into a string and concatenated.
Hence, the final output is 4312.89.

Option A

In JavaScript, the main difference between var and let lies in their scope. A variable declared with var has either global scope (if declared outside a function) or function scope (if declared inside a function). It does not follow block scope, meaning it can still be accessed outside the block { } in which it is defined.
On the other hand, a variable declared with let is block scoped, which means it is only accessible within the block { } where it is declared.
 

// Using var
if (true) {
    var x = 10;
}
console.log(x); // No Error, print 10 (var is not block scoped).
// Using let
if (true) {
    let y = 20;
}
console.log(y); // Error, y is not defined (let is block scoped).

Option C

JavaScript is primarily an interpreted language, and its code is executed by the JavaScript Engine inside a Web Browser such as Chrome, Firefox, etc. During execution, the browser reads the code and ignores comments because they are meant only for developers, not for execution.