Understanding the Weird Parts of JS

Question 1

syntax parser

Answer 1

a program that reads your code, determines what it does, and if its grammar (or syntax) is valid

Question 2

compiler

Answer 2

interpretors for computers so the computer understands your code and converts it into instructions

it goes through code character by character

Question 3

lexical environment

Answer 3

where something sits physically in the code you write

ie. a variable is on line 13 in the code

Question 4

execution context

Answer 4

a wrapper to help manage the code that is running

Question 5

object

Answer 5

a collection of name/value pairs

Question 6

global execution context

Answer 6

• the base execution context
• creates 2 things in our code by the JS engine:
  
  1. a global object
  2. a special variable ‘this’

Question 7

the window object

Answer 7

• the global object in browsers
• each window open in the browser has its own global object
• at the global level, the ‘this’ object is the same as the window object

Question 8

global

Answer 8

• not inside a function
• code or variables not within a function
• when you create variables + functions not inside a function, they get attached to the global object
• there is no outer environment at the global level

ex:
in code:
const a = ‘Hello world!”;

in the console:
a // => ‘Hello world!’
window.a // => ‘Hello world!’
this.a // => ‘Hello world!’

Question 9

execution context

Answer 9

table:

global object | ‘this’ | outer environment
_________________________________
your code!

Question 10

hoisting

Answer 10

setup memory space for variables and functions

• a function in its entirety is saved in memory
• a var name is saved (not the case for let or const)

Question 11

undefined

Answer 11

• a special value in JS
• the variable name exists, but the value has not been set, so JS sets the variable to the value ‘undefined’ and saves it to memory

Question 12

Uncaught referenceError: [var name] is not defined

Answer 12

means that a variable has not been declared and saved to memory

Question 13

single threaded synchronous execution

Answer 13

• single threaded: one at a time
• synchronous: one at a time in order

JS is executed line be line in the order of the code

Question 14

execution stack

Answer 14

• whichever execution context that is on top of the stack is the one that is currently running
• every time a function is called, it’s put on top of the stack
• once the function finished executing, it is removed from the stack