Eloquent Javascript Chapter 1: Values, Types, Operators

Question 1

Javascript vs. other languages

Answer 1

More liberal in what it allows. Good for flexibility, but makes it difficult to troubleshoot.

Question 2

Bits

Answer 2

All data is stored as bits, any kind of two-valued thing (usually 0’s and 1’s). The weight of each 0 or 1 increases from right to left.

Question 3

6 Types of Values

Answer 3

numbers, strings, Booleans, objects, functions, undefined values

Question 4

Javascript and accuracy re: fractional numbers

Answer 4

Calculations not always accurate because numbers are stored using 64 bits.

Question 5

Operators

Answer 5

Any symbol that causes an operation to occur: +, *, -, /, %

Question 6

% Operator

Answer 6

The remainder or modulo operator. X % Y provides the remainder of dividing X by Y.

Question 7

3 Special Numbers

Answer 7

Considered numbers but don’t behave like normal numbers: infinity, -infinity, NaN

Question 8

NaN

Answer 8

Not a number - results from any operation that doesn’t yield a precise result, such as 0/0, infinity-infinity, etc.

Question 9

Strings

Answer 9

Text in quotes. Can be marked with single and double quotes as long as beginning and end quotes match.

Question 10

Escaping the character

Answer 10

Need to “escape” the character with a backslash before certain characters, such as quotes within quotes and enters/newlines. \n = newline, \t = tab. Actual backslash is \.

Question 11

Concatenating strings

Answer 11

“text” + “text” = “texttext”

Question 12

Binary operators

Answer 12

Operators that take two values: 1-2, 2+3, 3>1

Question 13

Unary operators

Answer 13

Operators that take just one value. Includes operators that are not symbols, but words. Includes minus operator that can be used to make something negative. typeof() for example is a unary operator.

Question 14

console.log

Answer 14

Show result on screen. Ultimate appearance depends on Javascript environment chosen to run.

Question 15

Boolean values

Answer 15

Has only two possible values, true and false. console.log(3>2) results in true.

Question 16

Comparisons

Answer 16

Using >, <=, >=, ==, !=. Note that the latter two are imprecise and sometimes value types can be changed. Alternately, use === and !== for exact values.

Question 17

Can strings be compared with >,

Answer 17

Yes - they are compared based on Unicode standard, which assigns numbers to each character. Uppercase letters are valued less than lowercase ones.

Question 18

3 Logical operators

Answer 18

and (&&), or (||), not(!). These can be applied to Boolean values/used to reason about Booleans.

Question 19

&& vs. || precedence

Answer 19

&& has greater precedence than ||.

Question 20

Ternary operator

Answer 20

Choice between two values is decided by a third. true ? 1 : 2 will return left value, false ? 1 : 2 will return right value.

Question 21

2 Undefined values

Answer 21

null, undefined. Denote the absence of meaningful value, but are still values themselves. Are more or less interchangeable. Note that javascript might interpret null as 0. console.log(null==undefined) is true. console.log(null == 0) is false.

Question 22

Type coercion

Answer 22

When an operator is applied to the “wrong” type of value, JavaScript will convert that value to the type it wants, with often unexpected/unwanted results. If NaN appears where unexpected, may be result of accidental type conversions.

Question 23

Short-circuit evaluation

Answer 23

|| and && can return either left or right value. For ||, will return left value if it evaluates as true, else right value. && works opposite way, taking left if evaluates as false. This can be used to produce default values in the case that the left value evaluates as an NaN.