Javascript Foundation

Question 1

What is an Interpreter?

Answer 1

It’s what runs the code line by line.

Question 2

What is a Compiler?

Answer 2

A compiler translates code in one language to another language.

Question 3

What is Babel?

Answer 3

Babel is a Javascript compiler that takes your modern JS code and returns browser compatible JS (older JS code).

Question 4

What is Typescript?

Answer 4

Typescript is a superset of Javascript that compiles down to Javascript.

Question 5

What is a JIT Compiler?

Answer 5

Git Compiler is an engine that merges the interpreter and compiler together.

Question 6

What is Call Stack?

Answer 6

Call Stack is how the interpreter keeps track of the of its place in a script that has multiple functions. It keeps track of what function is currently being run and what functions are called from within that function.

Follows the first in the first out rule.

Question 7

What is Memory Heap?

Answer 7

Memory Heap is where the engine allocates memory to store data.

Question 8

What is Stack Overflow?

Answer 8

Is when the Call Stack has grown too large.

Question 9

What is Garbage Collection?

Answer 9

Garbage Collections is when the Javascript engine frees up allocated memory from objects no longer being used.

This doesn’t mean you shouldn’t care about memory management.

Question 10

What are the 3 most common ways to create a memory leak?

Answer 10

Global Variables

Event Listeners.

Set Interval.

Question 11

Javascript is a single-threaded language. What does single-threaded mean?

Answer 11

Single threaded means only one set of instructions is executed at a time.

Question 12

What is Javascript Runtime?

Answer 12

Javascript Runtime is the environment that houses the WebAPI, Callback Queue, Event Loop, and Engine.

Question 13

What is the Execution Context?

Answer 13

The ‘environment’ a function executes in.

Question 14

What is the Lexical Environment?

Answer 14

Where in the file your code is written in relation to the other code.

Think of like each function or code has its own world / its own lexical environment.

Question 15

What kind of function is in the picture?

Answer 15

Function Expression.

Question 16

What kind of function is in the picture?

Answer 16

Function Declaration.

Question 17

What is Hoisting?

Answer 17

Hosting is when variables with the keyword var and function declarations are moved to the top of their scope before code execution.

let and const do not get hoisted.

Variables with var are only partially hoisted. Meaning the variable gets hoisted but not the value of the variable.

Question 18

What is Function Invocation?

Answer 18

When you run the function.

Question 19

Explain undefined.

Answer 19

undefined means, Yes we have this variable but it is not assigned anything.

Question 20

Explain Reference Error.

Answer 20

Reference Error means this is completely undeclared. Scope chain can’t find anything.

Question 21

What is “use strict”?

Answer 21

The purpose of “use strict” is to indicate that the code should be executed in “strict mode”. With strict mode, you can not, for example, use undeclared variables.

Question 22

What is the this keyword?

Answer 22

this is the object that the function is a property of.

Question 23

If there is no object for this to refer to then what does it default to?

Answer 23

The window object.