Python \u2194 JavaScript Snippets

Quick reference for common Python patterns and their JavaScript equivalents.

35 snippets

Variable declarationVariables & Types

Python

x = 10
name = "Alice"

JavaScript

let x = 10;
let name = "Alice";

ConstantsVariables & Types

Python

MAX_SIZE = 100  # convention

JavaScript

const MAX_SIZE = 100;

Type checkingVariables & Types

Python

isinstance(x, int)
type(x).__name__

JavaScript

typeof x === "number"
typeof x

None / null / undefinedVariables & Types

Python

x = None
if x is None:

JavaScript

let x = null;
if (x === null) {}

String interpolationVariables & Types

Python

f"Hello, {name}!"

JavaScript

`Hello, ${name}!`

Multi-line stringVariables & Types

Python

"""line1
line2
line3"""

JavaScript

`line1
line2
line3`

List / ArrayCollections

Python

items = [1, 2, 3]
items.append(4)

JavaScript

const items = [1, 2, 3];
items.push(4);

Dictionary / ObjectCollections

Python

d = {"key": "value"}
d["key"]

JavaScript

const d = { key: "value" };
d.key // or d["key"]

DestructuringCollections

Python

a, b, c = [1, 2, 3]

JavaScript

const [a, b, c] = [1, 2, 3];

Spread / unpackCollections

Python

merged = [*a, *b]

JavaScript

const merged = [...a, ...b];

Dict mergeCollections

Python

merged = {**a, **b}

JavaScript

const merged = { ...a, ...b };

SetCollections

Python

s = {1, 2, 3}
s.add(4)

JavaScript

const s = new Set([1, 2, 3]);
s.add(4);

For loopLoops & Iteration

Python

for i in range(10):
    print(i)

JavaScript

for (let i = 0; i < 10; i++) {
  console.log(i);
}

For-eachLoops & Iteration

Python

for item in items:
    print(item)

JavaScript

for (const item of items) {
  console.log(item);
}

EnumerateLoops & Iteration

Python

for i, val in enumerate(items):
    print(i, val)

JavaScript

items.forEach((val, i) => {
  console.log(i, val);
});

List comprehension / mapLoops & Iteration

Python

squares = [x**2 for x in range(10)]

JavaScript

const squares = Array.from(
  {length: 10}, (_, x) => x ** 2
);

FilterLoops & Iteration

Python

evens = [x for x in nums if x % 2 == 0]

JavaScript

const evens = nums.filter(x => x % 2 === 0);

ReduceLoops & Iteration

Python

from functools import reduce
total = reduce(lambda a,b: a+b, nums)

JavaScript

const total = nums.reduce((a, b) => a + b);

Function definitionFunctions

Python

def greet(name):
    return f"Hello, {name}"

JavaScript

function greet(name) {
  return `Hello, ${name}`;
}

Lambda / arrow functionFunctions

Python

double = lambda x: x * 2

JavaScript

const double = (x) => x * 2;

Default argumentsFunctions

Python

def greet(name="World"):
    pass

JavaScript

function greet(name = "World") {}

Rest / *argsFunctions

Python

def func(*args):
    print(args)

JavaScript

function func(...args) {
  console.log(args);
}

Keyword / destructured argsFunctions

Python

def func(**kwargs):
    print(kwargs)

JavaScript

function func({ key, other }) {
  console.log(key, other);
}

If / elseControl Flow

Python

if x > 10:
    print("big")
elif x > 5:
    print("medium")
else:
    print("small")

JavaScript

if (x > 10) {
  console.log("big");
} else if (x > 5) {
  console.log("medium");
} else {
  console.log("small");
}

TernaryControl Flow

Python

result = "yes" if x else "no"

JavaScript

const result = x ? "yes" : "no";

Try / except / catchControl Flow

Python

try:
    risky()
except ValueError as e:
    print(e)

JavaScript

try {
  risky();
} catch (e) {
  console.log(e);
}

Class definitionClasses

Python

class Dog:
    def __init__(self, name):
        self.name = name

    def bark(self):
        return f"{self.name} barks!"

JavaScript

class Dog {
  constructor(name) {
    this.name = name;
  }

  bark() {
    return `${this.name} barks!`;
  }
}

InheritanceClasses

Python

class Puppy(Dog):
    def __init__(self, name):
        super().__init__(name)

JavaScript

class Puppy extends Dog {
  constructor(name) {
    super(name);
  }
}

Async functionAsync

Python

import asyncio

async def fetch():
    await asyncio.sleep(1)
    return "data"

JavaScript

async function fetchData() {
  await new Promise(r => setTimeout(r, 1000));
  return "data";
}

Promise / FutureAsync

Python

result = await fetch_data()

JavaScript

const result = await fetchData();

Print / logCommon Operations

Python

print("Hello")

JavaScript

console.log("Hello");

String methodsCommon Operations

Python

"hello".upper()
"HELLO".lower()
"hello world".split()

JavaScript

"hello".toUpperCase()
"HELLO".toLowerCase()
"hello world".split(" ")

Array/list sliceCommon Operations

Python

items[1:3]
items[::-1]  # reverse

JavaScript

items.slice(1, 3)
[...items].reverse()

JSON parse/stringifyCommon Operations

Python

import json
data = json.loads(s)
s = json.dumps(data)

JavaScript

const data = JSON.parse(s);
const s = JSON.stringify(data);

Date / timeCommon Operations

Python

from datetime import datetime
now = datetime.now()

JavaScript

const now = new Date();

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Python \u2194 JavaScript Snippets

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