JavaScript/TypeScript vs Python Crib Sheet

1. Variables and Data Types

Concept	JavaScript / TypeScript Example	Python Example
Declare variable (let, const)	let x = 5; const y = 10;	x = 5
Declare object	let obj = { name: "John" }	obj = { "name": "John" }
Declare array	let arr = [1, 2, 3];	arr = [1, 2, 3]
Array of objects	let arr = [{name: "A"}, {name: "B"}];	arr = [{"name": "A"}, {"name": "B"}]
Null	null	None
Undefined	undefined	None (used in place of undefined)
True/False	true, false	True, False

2. Objects vs Dictionaries

Concept	JavaScript / TypeScript	Python
Create object	let obj = { key: "value" }	obj = { "key": "value" }
Access object value	obj.key or obj["key"]	obj["key"]
Add/update key	obj.newKey = "newValue"	obj["newKey"] = "newValue"
Delete key	delete obj.key	del obj["key"]

3. Arrays vs Lists

Concept	JavaScript / TypeScript	Python
Create array/list	let arr = [1, 2, 3];	arr = [1, 2, 3]
Access element	arr[0]	arr[0]
Add element	arr.push(4)	arr.append(4)
Remove element	arr.pop()	arr.pop()
Array length	arr.length	len(arr)
Loop through array	arr.forEach(item => console.log(item))	for item in arr: print(item)

4. Spread Operator / Unpacking

Concept	JavaScript / TypeScript	Python
Spread array	let newArr = [...arr, 4];	new_arr = [*arr, 4]
Spread object	let newObj = {...obj, newKey: "new"}	new_obj = {**obj, "newKey": "new"}
Spread function args	function(...args) {}	def function(*args):

5. Conditionals and Null/True Operations

Concept	JavaScript / TypeScript	Python
If statement	if (condition) {}	if condition:
Ternary	let val = condition ? trueVal : falseVal	val = trueVal if condition else falseVal
Nullish coalescing operator	let val = x ?? "default";	val = x or "default"
Optional chaining	let val = obj?.key;	val = obj.get("key") or val = obj["key"] if obj else None

6. Loops

Concept	JavaScript / TypeScript	Python
For loop	for (let i = 0; i < arr.length; i++) {}	for i in range(len(arr)):
For…of loop (array)	for (let item of arr) {}	for item in arr:
For…in loop (object keys)	for (let key in obj) {}	for key in obj:
While loop	while (condition) {}	while condition:

7. Functions

Concept	JavaScript / TypeScript	Python
Declare function	function myFunc() {}	def my_func():
Arrow function	const myFunc = () => {}	N/A (use def my_func():)
Return	return value;	return value
Default parameter	function myFunc(a = 10) {}	def my_func(a=10):
Rest parameters	function(...args) {}	def function(*args):

8. Classes and Objects

Concept	JavaScript / TypeScript	Python
Declare class	class MyClass {}	class MyClass:
Constructor	constructor()	def __init__(self):
Instance method	this.myMethod()	self.my_method()
Create object	let obj = new MyClass();	obj = MyClass()

9. Error Handling

Concept	JavaScript / TypeScript	Python
Try/Catch	try { ... } catch (e) { ... }	try: ... except Exception as e:

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Key Differences to Keep in Mind:

1. None vs. null/undefined: In Python, None represents both null and undefined in JavaScript. There’s no separate undefined in Python.
2. Indentation matters: Python uses indentation to define blocks of code (no curly braces).
3. No semi-colons: Python doesn’t require semi-colons at the end of statements.
4. True/False: Use True and False in Python (capitalized), not true and false as in JavaScript.
5. Method definition: When defining a class method, you need to include self as the first argument in Python, which refers to the instance of the class.