Differences between JavaScript and Python

notes.md

Data Types

Python	JavaScript
String immutable	String immutable
Integer whole numbers Float decimals	Number - includes NaN and Infinity
	Bigint - for integer values larger than 2^53 or less than -2^53 - in Jan 2020, not fully supported by all browsers
Boolean - True and False are capitalized	Boolean - true and false are lowercase
Dictionary	Object - includes Array, null, RegExp, Math, Map, WeakMap, Set, WeakSet, Intl, Reflect, WebAssembly, and JSON
	undefined
	Function - includes Date, Promise, ArrayBuffer, DataView, Proxy, and Error - arguments is an array-like object available inside of a function
	Symbol
List: similar to an array
Tuple: similar to a list, but immutable and order matters e.g (1, 3, 20) could represent hours, minutes, and seconds

Type Checks and Type Conversion

	Python	JavaScript
check type with	type()	typeof
to a string	str()	data.toString() or type coercion by concatenation
to a number		parseInt() - expects a string and parses up to the first non-digit and returns whatever it parsed - The second param, radix, is 10 by default Number() - will parse any type and try to convert it to a number - returns NaN if it can't convert it to a number

Comparisons and Logical Operators

	Python	JavaScript
equal	==	===
not equal	!=	!==
not	not	!
or	or	||
and	and	&&

Loops

	Python	JavaScript
you can break out of while and for loops	yes	yes
for loops start with...	0, for x in range(5) iterates 0-4 pass two params to indicate a different starting point for x in range(1, 5) pass a third param to change the step for x in range(1, 5, 2) Note that 5 is not inclusive	whatever is defined, for(var i = 0; i < 5; i++){} for - loops through a block of code a number of times for/in - loops through the properties of an object for/of - loops through the values of an iterable object

Functions

	Python	JavaScript
define a function	def functionName():	function functionName() {} or () => {} or assign the function to a var to name it
return value if no return value is specified	none	undefined
what can be returned	multiple values	one value
scoped self reference	self	this

Strings

	Python	JavaScript
check the length of a string	len(<string>)	<string>.length
iterate over each character in a string	for character in string
access the char at index i starting at zero	<string>[i]
access the substring at index i ending at index j-1	<string>[i:j] If i is omitted, default is 0. If j is omitted, default is len(string).
index of a char	<string>.index	<string>.indexOf
slice of a string	<string>[0:3]	<string>.slice(0, 3)
includes	if <substring> in <string>	'<string>'.includes('<substring>')
lowercase	<string>.lower()
uppercase	<string>.upper()
remove white space	left: <string>.lstrip() right: <string>.rstrip() both:<string>.strip()
the number of times substring is present in the string	<string>.count(<substring>)
only numeric characters, returns boolean	<string>.isnumeric())
only alphabet characters, returns boolean	<string>.isalpha())
split	<string>.split(<delimiter>))
replace all occurrences returns a new string	<string>.replace(<old>, <new>))
join a list of strings returns a new string	<delimiter>.join(<list of strings>)

Sequences (Lists/Tuples | Arrays)

	Python	JavaScript
return the length of a sequence	len(<list>)	<array>.length
iterate over each element in the sequence	for <element> in <sequence>
check if an element is in a sequence	if <element> in <sequence>
access the element at index i i starts at zero	<sequence>[i]
access the substring at index i ending at index j-1	<sequence>[i:j] If i is omitted, default is 0. If j is omitted, default is len(string).
iterate over both the indexes and the elements	for index, <element> in enumerate(<sequence>)
add an item	<list>.append('item')	<array>.push('item')
insert an item	<list>.insert({index, 'item')

• use list comprehension to create a list [<expression> for <variable> in <sequence> if <condition>] e.g.: [x for x in range(0, 101) if x % 3 == 0]

Lists || Array

	Python	JavaScript
return the length of a sequence	len(<list>)	<array>.length
replaces the element at index i with x	<list>[i]	<array>[i]
inserts x at the end of the list	<list>.append(x)	<array>.push(x)
inserts x at index i	<list>.insert(i, x)
returns the element a index i, also removing it from the list	<list>.pop(i)
removes the first occurrence of x	<list>.remove(x)
sorts the items	<list>.sort() .sort modifys the list, use sorted(<list>, <key>) to return a new list
reverses the order of items	<list>.reverse()
removes all the items	<list>.clear()
creates a copy of the list	<list>.copy()
appends all the elements of other_list at the end of list	<list>.extend(other_list)

Dictionaries | Objects

	Python	JavaScript
delete a property	delattr(<obj>, <property>) and del <obj>.<property>	delete <obj>.<property>
key names	can be any immutable data type: numbers, booleans, stings, or tuples	strings or symbols
iterates over each key in the dictionary	for key in <dictionary>
iterates over each key,value pair in the dictionary	for key, value in <dictionary>.items()
checks whether the key is in the dictionary	if key in <dictionary>
accesses the item with key key of the dictionary	<dictionary>[key]
sets the value associated with key	<dictionary>[key] = value
returns the element corresponding to key, or default if it's not present	<dictionary>.get(key, default)
returns a sequence containing the keys in the dictionary	<dictionary>.keys()
returns a sequence containing the values in the dictionary	<dictionary>.values()
updates the dictionary with the items coming from the other dictionary. Existing entries will be replaced; new entries will be added.	<dictionary>.update(<other_dictionary>)
removes all the items of the dictionary	<dictionary>.clear())

Classes

	Python	JavaScript
print properties and methods of a class	dir(<type or class>)
print properties and methods of a class including arguments and function definitions	help(<type or class>)
create a class without properties	class <capitalized class name> pass
create a class with properties	class <capitalized class name> color = ''
create a class with a method	class <capitalized class name> def <function_name>(self):
constructor	class <capitalized class name> def __init__(self, <additional params>):
create a print friendly message for an object	class <capitalized class name> def __self__(self):
Docstring	"""a brief text in the first line of the function definition that explains what a function does wrapped in triple quotes"""

• instance variables: Variables that have different values for different instances of the same class
• if you try to print an object, it will print the location in the computer's memory
• docstring is a brief text that explains what something does
• always initialize mutable attributes in the constructor

Modules

	Python	JavaScript
import a module to use, e.g. random, datetime, timedelta...	import <module>

Misc

	Python	JavaScript
comment out code	#	// or for long sections /* comment */
else if conditions	elif	else if
end param inside of print	acts like a line break in a print statement	NA
max recursive function calls the language allows	1000