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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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About Python to JavaScript

Convert simple Python snippets into equivalent JavaScript to speed up porting and learning. Handles common syntax like prints, loops, and basic data structures as a starting point.

How to use

  1. Paste a Python snippet.
  2. Review the generated JavaScript.
  3. Adjust library-specific calls that have no direct JS equivalent.

Frequently asked questions

Will it convert any Python program?
It handles common syntax as a head start; framework- and library-specific code usually needs manual adjustment.
Does it convert indentation to braces?
Yes — Python’s block indentation is translated into JavaScript’s brace-delimited blocks.