chrome version 49.0.2623.110 m

node v5.10.0

Here is my code:

var a = 0;

(function() {
    this.a = 1;
    this.b = 2;
    console.log(a);
} )();

console.log(a);
console.log(b);

chrome gives

1
1
2

node gives

0
0
2

Why does that happen?

Thanks

chrome version 49.0.2623.110 m

node v5.10.0

Here is my code:

var a = 0;

(function() {
    this.a = 1;
    this.b = 2;
    console.log(a);
} )();

console.log(a);
console.log(b);

chrome gives

1
1
2

node gives

0
0
2

Why does that happen?

Thanks

• javascript
• node.js
• google-chrome

• 1 It has nothing to do with V8, but the way global scope works in Node, and in browsers (where the global scope is window). Try console logging this, and it should bee clear. – adeneo Commented Apr 4, 2016 at 16:44

1 Answer 1

When a function is called without context (and you are running in non-strict mode) this defaults to the global object.

In a browser the top-level of your source code runs in the global context, so this.a, which is window.a is the same as the var a declared in the global context at the top. Assigning this.a = 1 is the same as assigning a = 1.

In node.js each JavaScript file gets its own module context that is separate from the global context, so var a = 0; is not creating a global, and the global you created with this.a = 1; will be shadowed by the modules own a.