js_flashcards_hoisting

Question 1

What is hoisting in JavaScript?

Answer 1

Hoisting is a mechanism where variable and function declarations are conceptually moved to the top of their scope before execution. Only declarations are hoisted, not initializations.

Question 2

How are var variables hoisted?

Answer 2

Hoisted to the top and initialized with undefined. Accessible before declaration but value is undefined.

Question 3

How are let and const variables hoisted?

Answer 3

They are hoisted but not initialized. They exist in the Temporal Dead Zone (TDZ) until declaration. Access before declaration throws ReferenceError.

Question 4

What is the Temporal Dead Zone (TDZ)?

Answer 4

The period between entering a scope and the declaration of let/const. Accessing variables in TDZ causes ReferenceError.

Question 5

How are function expressions hoisted?

Answer 5

Depends on assignment. If var: variable is hoisted with undefined (calling before assignment causes TypeError). If let/const: subject to TDZ (ReferenceError).

Question 6

What is a common pitfall with var and hoisting?

Answer 6

Access before assignment results in undefined, leading to unexpected behavior.

Question 7

Benefits of let and const over var in relation to hoisting?

Answer 7

TDZ enforces declaring before using, promoting cleaner code and reducing bugs. They also support block scoping.

Question 8

How does hoisting affect code readability?

Answer 8

Makes code harder to understand. Best practice: declare variables at the top for clarity.

Question 9

Best practice for function declarations and hoisting?

Answer 9

Even though hoisted, define functions before calling for clarity and organization.

Question 10

How does hoisting interact with block scope?

Answer 10

var is function-scoped, ignoring block scope. let and const are block-scoped, important for hoisting and TDZ.

Question 11

How does Strict Mode prevent accidental globals?

Answer 11

Assigning to undeclared variables throws ReferenceError instead of creating globals.

Question 12

Common errors in Strict Mode?

Answer 12

ReferenceError (undeclared vars), TypeError (illegal assignments), SyntaxError (duplicate parameters).

Question 13

Examples of good and bad variable names?

Answer 13

Good: getUserById, totalPrice, isValid.
Bad: getU, tp, isV.
Use camelCase, PascalCase for classes, UPPER_SNAKE_CASE for constants.

Question 14

How do const and let improve code over var?

Answer 14

const: prevents reassignment.
let: block scoped.
var: function scoped, can cause unexpected behavior.

Question 15

Two restrictions in Strict Mode?

Answer 15

Disallows with statement, deleting undeletable properties.

Question 16

What is a ReferenceError?

Answer 16

Occurs when accessing undeclared/unavailable variable at runtime.

Question 17

What is an Execution Context?

Answer 17

Environment for executing JS code: contains variables, functions, this.

Question 18

What is the Function Execution Context?

Answer 18

Created each function call with its variables, arguments, this.

Question 19

Heap vs Stack in JS memory?

Answer 19

Heap: dynamic data (objects, arrays).
Stack: static data (function calls, vars).

Question 20

Explain mutability in JS.

Answer 20

Primitives immutable. Reference types mutable. const prevents reassignment but not mutation.

Question 21

How to prevent accidental globals?

Answer 21

Always declare with var/let/const. Use ‘use strict’.

Question 22

Where are objects/arrays stored?

Answer 22

In the heap, with variables holding references.

Question 23

How to prevent accidental globals?

Answer 23

Declare with var/let/const. Use Strict Mode.