JavaScript was born for browser, it’s the the only language that browsers natively understand for client-side scripting.

// JavaScript was literally created for web browsers in 1995
<script>
    document.getElementById("myButton").onclick = function() {
        alert("Hello World!");
    };
</script>

In 2009, it was expanded to run on servers by node.js runtime, which was built on Chrome’s V8 engine.

// Node.js (2009) brought JavaScript to servers
const express = require('express');
const app = express();

app.get('/', (req, res) => {
    res.send('Hello from JavaScript server!');
});

app.listen(3000);

While Python is a different story, no browser understand/talk to Python, browser deals with html on structure, with css on style and with javascript on behavior.

Python is scripting language, but Javascript even the name has script, is more like compiling language, Browser has JS engine built-in. So Why Browsers Have Built-in JavaScript Interpreters?

When web pages was static, it’s boring, so Brendan Eich created JavaScript in just 10 days (May 1995). The goal is to Make web pages interactive with simple scripting. NetScape designed with the thought

// Easy syntax that HTML authors could learn
onclick="alert('Hello!')"

// Not this complex Java:
public class HelloWorld {
    public static void main(String[] args) {
        System.out.println("Hello World");
    }
}
<script>
    // JavaScript code goes right in the HTML
    document.write("Today is " + new Date());
</script>

<!-- Not a separate compiled program -->
// Runs immediately, no compilation step
<script>
    if (new Date().getHours() < 12) {
        document.body.style.backgroundColor = 'lightblue';
    }
</script>

Lastly JavaScript runs in a secure sandbox.

The key insight: JavaScript wasn’t necessarily the “best” language – it was the right language at the right time that solved the specific problem of making web pages interactive.

Once millions of websites used JavaScript and developers learned it, changing would break the entire web. So every new browser had to support JavaScript to be compatible.

This created a path dependency – a historical decision that locked in JavaScript as the web’s scripting language, leading to its dominance across all platforms today.