Declarations

Question 1

Syntax to declare variable with block scope? (2)

Answer 1

Let - declares a block scope local variable, optionally initializing it to a value. *Let cannot declare a variable at global scope.
Const - declares read-only variable with block scope

Question 2

Limitations to variables declared with ‘Let’

Answer 2

• not hoisted; temporal availability when block is executed
• cannot create variable on global object
  ex: Cannot check properties outside of block; cannot access within block statements like Switch{ }
• backwards compatibility issues (ES6+)

Question 3

When are double quotes required in JavaScript?

Answer 3

JSON requires double quotes for strings

Question 4

What is wrong with this syntax?

var a=b=c=10 ;

Answer 4

b and c are global variables. oops

• Do not chain var declaration AND assignments
  var a, b, c; //ok

Question 5

What is the scope of a parameter passed to a function?

Answer 5

Parameters are local variables (no need to re-assign to var within the function body).
- A parameter passed to a parent function will be in closure scope (is known to IIFE it returns)

Question 6

Are identifiers case-sensitive?

Answer 6

Yes

Question 7

“typeof” operator applies to?

Answer 7

Primitives

Question 8

“instanceof” operator applies to?

Answer 8

Objects

Question 9

What is a statement, and how can it be identified?

Answer 9

Statements “do things”. A sequence of statements is a program.

To prevent ambiguity, terminate statements with semicolon ;

Question 10

What is the diff between a statement and an expression? Are they interchangeable?

Answer 10

Expressions produce values

- Expressions can be used where a statement is expected (“expression statement” ends with a ‘;’)

Question 11

How does JS differentiate a block statement from an expression?

Answer 11

• Expressions cannot start with curly brace { }
• Expressions cannot start with function keyword
• Block statements do NOT end with semi-colon

The following are block statements:
{
foo: bar(3, 5)
}

function foo() { }

Question 12

How do you turn a block statement into an expression? Examples?

Answer 12

( ) can transform blocks into expressions
ex.1: Object literal ({dog:Floyd})

Create function expression ending with semicolon
var f = function( ){ }; 

Create IIFE with parentheses and semicolon
(function( ) { …})( );

Question 13

What is ‘lexical scoping’ ?

Answer 13

The word “lexical” refers to the fact that lexical scopinguses thelocation where a variable is declared within the source code to determine where that variable is available.Nested functions have access to variables declared in their outer scope.