JavaScript vs Python: A Side-by-Side Syntax Guide

JavaScript and Python are the two most popular programming languages in 2025. If you know one, learning the other is surprisingly fast — once you map the concepts.

Variables

| JavaScript | Python |

|---|---|

| `const x = 5;` | `x = 5` |

| `let y = 10;` | `y = 10` |

| `var z = 15;` | *(avoid — no equivalent)* |

Functions

// JavaScript
function greet(name) {
  return `Hello, ${name}!`;
}
const double = x => x * 2;

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

double = lambda x: x * 2

Arrays / Lists

const nums = [1, 2, 3];
const doubled = nums.map(n => n * 2);
const evens = nums.filter(n => n % 2 === 0);

nums = [1, 2, 3]
doubled = [n * 2 for n in nums]
evens = [n for n in nums if n % 2 == 0]

Objects / Dicts

const user = { name: "Alice", age: 30 };
user.name; // "Alice"

user = {"name": "Alice", "age": 30}
user["name"]  # "Alice"

Classes

class Dog {
  constructor(name) { this.name = name; }
  bark() { return `${this.name} says woof!`; }
}

class Dog:
    def __init__(self, name):
        self.name = name
    def bark(self):
        return f"{self.name} says woof!"

Async

Both use async/await syntax. The main difference is the runtime:

Bottom Line

The concepts are nearly identical. The syntax is ~80% different. Use codemirr's Mirror Courses to learn the differences systematically.