What should I do to understanding this case? (nodejs)

Question

in nodejs REPL

$ node
> var a = 10;
undefined
> console.log(this.a);
10

---

in execute > node test.js

// test.js
var a = 20;
console.log(this.a);

$ node test.js
undefined

What is different this context from 'repl vs execute js file'?

in execute, console.log(this) -> just {}

not global context