Basics

Question 1

JS statement

Answer 1

A statement is an instruction for the computer to do something ie let x=10. function calls and assignments are included in MDN but not the official specs

Question 2

JS expression

Answer 2

an expression is a bit of JavaScript code that produces a value which can be captured for later use

Question 3

What is undefined?

Answer 3

We can describeundefined as representing the absence of a value. can arise implicitly.

Question 4

What is null?

Answer 4

nullrepresents emptiness or nothing. null can’t arise implicitly. While null is a primitive, typeOf(null) returns object.

Question 5

What is a literal?

Answer 5

A literal is any notation that lets you represent a fixed value in source code

Question 6

give some examples of literals

Answer 6

‘Hello, world!’ // string literal
3.141592 // numeric literal
true // boolean literal
{ a: 1, b: 2 } // object literal
[ 1, 2, 3 ] // array literal
undefined // undefined literal

Question 7

What is are the truthy values in JS?

Answer 7

Numbers other than 0 and NaN
Non-empty string values
All objects

Question 8

What are the falsy values in JS

Answer 8

0, -0, 0n
‘’ or “”
NaN, null, undefined
The document.all global object

Question 9

What is short circuit evaluation?

Answer 9

this means expressions are evaluated from left to right until it is confirmed that the result of the remaining conditions is not going to affect the already evaluated result

Question 10

what’s the difference between properties and methods on JS data types?

Answer 10

A property says something about the value and a method does something with that value

Question 11

What are the two kinds of methods and how are they different?

Answer 11

Instance methods and static methods.
- you apply instance methods to a value of the type that the constructor represents (ie ‘hello’.toUpperCase())

You apply static methods to the types constructor itself (ie String.fromCharCode(97))

Instance methods are designated with a .prototype.method()

Question 12

What are the 5 primitive data types in JS?

Answer 12

String, Number, Undefined, Null, and Boolean. Every type that is not a primitive is an object type.

Question 13

What is a template literal?

Answer 13

They use backticks (`) and enable string interpolation

Question 14

Are there any values in JS that can’t equal themselves in comparison operations?

Answer 14

NaN is the only value is JS that cant equal itself

Question 15

How should you test if something is a NaN

Answer 15

Use Number.isNaN(value)

Question 16

what happens when you use the + operator with a string and anything else?

Answer 16

if either operand is a string and the other is not, JavaScript coerces the non-string operand to a string; thus, the result is always another string.

Question 17

How do you turn a string into a number?

Answer 17

You can use Number(’13’) to explicitly coerce a string to number form. You can also use parseFloat() or parseInt() if the string contains non-numerical data.

Question 18

What is an array? What are their defining attributes?

Answer 18

• uses square brackets[ ]surrounding a comma-delimited list of values
  
  • Can contain any data type in an ordered list
• Indexed from 0 using a second pair of square brackets

Question 19

What happens if you attempt to access a nonexistent array index?

Answer 19

No error will be throw. JS will simply return undefined.

Question 20

What is an Object and what are their key attributes

Answer 20

• Organized by key-value pairs, with each pair consisting of a key, in the form of a string, and a value of any type.
• object literals have zero or more key-value pairs separated by commas all embedded within curly braces
• values are accessed by key rather than index

Question 21

How do you access an objects information?

Answer 21

using dot or square bracket notation. Note that if you wish to use a variable storing the key you must use bracket notation.

Question 22

how do you tell JS that the next char isn’t syntactic but is part of a string?

Answer 22

you can use the \ escape char