Fundamentals

Question 1

The Six Primitive Values

Answer 1

numbers, strings, booleans, objects, functions, and undefined values

Question 2

Arithmetic Operators

Answer 2

\+    Plus       Addition
-    Minus     Subtraction
*    Star        Multiplication
/    Slash      Division
()    Parens    Grouping
%   Percent  Modulus or Remainder

Question 3

Special Number Values

Answer 3

Infinity Positive Infinity
-Infinity Negative Infinity
NaN Not a number

All three are special values considered of the number type but don’t behave like other numbers.

Question 4

NaN == NaN

Answer 4

false

NaN is the only value in JS that is NOT equal to itself.

Question 5

Logical Operators

Answer 5

&& (AND)
|| (OR)
! (NOT)

Question 6

The Ternary Operator

Answer 6

( v1 ? v2 : v3 )

IF ‘first value’ THEN ‘second value’ ELSE ‘third value’

Question 7

===

!==

Answer 7

Precision equality. JS will not attempt any type coercion when comparing using either of these two operators. Items compared with == and != are subject to type coercion.

Question 8

The var statement

Answer 8

var name;
var name = expression;
var n1 = ex1, n2 = ex2;

A variable name with no assigned expression is evaluated as ‘undefined’.

Question 9

Valid variable names

Answer 9

Are alphanumeric, must begin with a letter, and may contain underscore ‘_’ or dollar sign ‘$’ but no other punctuation or whitespace.

Question 10

Coercion functions

Answer 10

Number()
String()
Boolean()

Question 11

How do I check if a value is not a number or cannot be converted to a number?

Answer 11

isNaN(value) –> true
* or *
isNaN(Number(value)) –> true
Number(value) returns NaN if the value cannot be converted.

Question 12

‘do … while’ loops

Answer 12

do {statements} while (expression);

Do statements at least once, then keep doing them until expression evaluates as false.

Question 13

‘for’ loops

Answer 13

for (initialization; check; update) { statements; }

Question 14

‘while’ loops

Answer 14

while (expression) { statements; }

Question 15

break

Answer 15

Control jumps out of the enclosing loop.

Question 16

continue

Answer 16

Control jumps out of the loop body and the loop begins again at the beginning.

Question 17

switch

Answer 17

switch (expr) {
   case label_1:
   statements;
   [break];
   ...
   case label_2:
   ...
}

Question 18

if and else statements

Answer 18

if (expression) { statement; }
else if (expression) { statement; }
else { statement; }

Question 19

function statement

Answer 19

var func_name = function (params) { body; };

The curly braces are not optional, no matter how short the body is.

Question 20

function declaration

Answer 20

function name (params) { body; };

A function may be declared anywhere in the scope and calls to it will still work. Function declarations are read before execution begins.

Question 21

“Optional” function arguments

Answer 21

If args > parameters, then the additional arguments are ignored. If args < parameters, the missing parameters are assigned the value undefined.

Question 22

Arrays

Answer 22

Store an ordered sequence of values. Array literals are created by separating the values with commas and wrapping the whole in square brackets.

Question 23

Getting Properties

Answer 23

Two ways. Direct naming via dot notation and evaluative access via square brackets.

Question 24

Methods

Answer 24

properties that contain function values are called methods.

Question 25

Objects

Answer 25

Arbitrary collections of properties. Syntax:
var object_name = {
    'prop name': value_expression,
   prop2: val_exp,
};

Question 26

The delete operator

Answer 26

A unary operator that deletes a property from an object.

delete obj_name.prop_name
delete obj_name[“prop name”]

Question 27

Object property assignment

Answer 27

obj_name[“prop_name”] = value

will assign the value to the property of the object. If the property does not exist it is created.

Question 28

The in operator

Answer 28

“string” in object

A binary operator applied to a string and an object that will return true if the string names a property of the object.

Question 29

Mutable and Immutable values

Answer 29

Objects are mutable. Arrays are a special case of objects, therefore they are mutable.

Numbers, Strings, and Booleans are Immutable.

Question 30

Object Comparison

Answer 30

name1 == name2 will return true only if both object names refer to the same object, false otherwise - even if name1 and name2 refer to separate objects that have identical contents. There is no ‘deep’ comparison operator built-in.

Question 31

Looping over the properties of an object

Answer 31

for (var elem in object) {
do whatever to elem;
do whatever to object[‘elem’];
}

This is very pythonic - essentially a python for statement. It loops over the elements of the object.

Question 32

The arguments object

Answer 32

When a function is called, a special variable named arguments is created for that local environment - it stores the arguments that were passed to the function. The arguments object is a lot like an array but it supports no array methods. It does however have a length property and it’s elements can be accessed via index (i.e. arguments[x] gets the value at x).

Question 33

The Math object

Answer 33

A container for a bunch of mathematical stuff. Properties:
max
min
floor
ceil
round
PI
random
* trig stuff --> sin, cos, tan, etc.

Question 34

The Global object

Answer 34

The object where each global variable is stored. In browsers, the global scope object is stored in the window variable.

Question 35

JSON

Answer 35

JavaScript Object Notation
Very similar to objects and arrays with some restrictions:
1. All property names are wrapped in double quotes
2. No comments allowed.
3. Only simple data types - no function calls, etc.

Question 36

JSON.stringify(value)

Answer 36

takes a JS value and returns a JSON encoded string

Question 37

JSON.parse(string)

Answer 37

Takes a JSON encoded string and returns the value it encodes.