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3. Literals, Variables, Constants, & Data Types

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What is a constant?

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Mar 1, 2020

Cards (45)

Section 1

(45 cards)

What is a constant?

Front

holds a value, but unlike a variable, the value can't change after initialization

Back

How do you initialize a date to a specific date?

Front

const halloween = new Date(2016, 9, 31);

Back

How do you initialize a date to the current date or time?

Front

const now = new Date(); now;

Back

What are the naming rules for identifiers?

Front

1. must start with a letter, dollar sign ($), or underscore (_) 2. consist of letters, numbers, the dollar sign ($), & underscore (_) 3. unicode characters are allowed 4. cannot be a reserved word

Back

What is the advantage of using parseInt?

Front

it allows you to specify a radix which is the base with which you want to parse the number, such as specifying base 16 to parse hexadecimal numbers

Back

What is a map?

Front

map keys to values (like objects) but offer some advantages in certain situations also can't contain duplicates

Back

How do you convert to a string?

Front

the toString method

Back

What are identifiers?

Front

variable, constant, & function names

Back

What character is used to escape strings?

Front

backslash

Back

What is the naming convention for constants?

Front

It is conventional (but not required) for constants that refer to specific number or string to be named with all uppercase letters and underscores

Back

What are regular expressions?

Front

a common language extension that represents a compact way to perform complex search & replace operations on strings

Back

Can an object contain a function as one of its properties?

Front

yes

Back

What's the literal syntax of an object?

Front

curly braces {}

Back

What special 3 values result in numeric values that are not numeric literals?

Front

1. NaN 2. negative infinity 3. infinity

Back

When do you always want to use a variable and not a constant?

Front

loop control

Back

What is variable declaration?

Front

creating a variable with var, let, or const

Back

How do primitives and objects differ?

Front

primitive types are immutable while objects can take on different forms and values

Back

Booleans evaluate to what two values?

Front

true & false

Back

If you don't provide an initial value for a variable when you declare it, what special value does it get?

Front

undefined

Back

What does JSON stand for?

Front

JavaScript Object Notation

Back

What format does JavaScript use to approximate real numbers?

Front

double (double-precision floating-point)

Back

What's the difference between null & undefined?

Front

null is a data type available to you the programmer undefined should be reserved for JS itself (best practice, but not a rule)

Back

How do you declare multiple variables with the same let statement?

Front

use commas, e.g. let var1, var2 = "example_value", var2 = "second_example_value"

Back

How can strings be converted to numbers?

Front

1. const numStr = "33.3"; const num = Number(numStr); 2. use the built-in parseInt or parseFloat

Back

What makes arrays special (vs regular objects)?

Front

array contents have a natural order (element 0 will always come before element 1), & keys are numeric & sequential

Back

What are symbols?

Front

a data type representing unique tokens, similar to objects in that each is unique

Back

What is the advantage of using a constant (vs a variable)?

Front

It makes it harder to accidentally change the values of things that shouldn't be changed

Back

What are the contents of an object called?

Front

properties (or members)

Back

What is Number.EPSILON?

Front

smallest number that can be added to 1 to get a distinct number

Back

How do sets differ from arrays?

Front

sets cannot contain duplicates

Back

What is a trailing comma?

Front

a comma at the end of multiple elements spanning multiple lines inside an array or object

Back

What is a string template?

Front

provides a shorthand way of injecting values into a string e.g. `The current temperature is ${currentTemp} \u00b0C`

Back

What's another name for a string template?

Front

string interpolation

Back

What are the built-in object types (mentioned in this chapter)?

Front

1. array 2. date 3. regexp 4. map / weakmap 5. set / weakset

Back

When do you use the computed member access operator?

Front

when you want property names that are not valid identifiers, e.g. obj["not an identifier"] = 3;

Back

Are array elements required to have the same type?

Front

no, they are not homogenous

Back

How would you get the first element of this array called "arr": ['a', 'b', 'c'] ?

Front

arr[0]

Back

What do strings represent in JavaScript?

Front

unicode text

Back

How do you convert to boolean?

Front

use the not operator (!) twice

Back

What is a variable?

Front

named value that chan change at any time

Back

What do properties consist of?

Front

1. name (key) 2. value

Back

What is a literal?

Front

means that you're providing the value directly to the program; JavaScript takes the literal value you provide and creates a data value from it

Back

What does camel case refer to?

Front

convention for naming JavaScript identifier that starts with lower case and capitalizes following words: "camelCase"

Back

What 4 types of numeric literal does JavaScript recognize?

Front

1. decimal 2. binary 3. octal 4. hexadecimal

Back

What are the 6 primitive types?

Front

1. number 2. string 3. boolean 4. null 5. undefined 6. symbol

Back