How is the global object in Node.js different from the window object in the browser?

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The global object in Node.js often gets compared to the window object in the browser but they're not quite the same.

First, let's understand what the window object is before comparing it to the global object.

The window object

In the browser, the window object is sometimes referred to as the global scope because any properties that exist on it can be used anywhere within your code, including any you create. This is the top-level scope of our JavaScript code.

var a = 'Global scope'; or // window.a = 'Global Scope'

const myFunc = () => {
  console.log(window.a); // 'Global scope'
  console.log(a); // or just leave out 'window'
};

Notice how the use of window as a prefix to access these properties is optional but encouraged for readability.

The global object

In Node.js, the global object is different. It doesn't refer to the global scope in the same way window does in the browser.

In this situation, global refers to a global namespace but it's the not top-level scope for defining and using variables / properties.

var a = 'Not the global scope';

const myFunc = () => {
    console.log(global.a); // undefined
    console.log(a); // Not the global scope
};

This is because the top-level scope in Node.js is the current module you are working in. So variables declared as in the example above, will be local to that module.

let and const

Using let or const to define a variable either in the browser will change how things work:

let a = 'Block scope';

const myFunc = () => {
  console.log(window.a); // undefined
  console.log(a); // 'Block scope'
};

This is due to block scoping in ES6.

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