module.exports and scope in javascript

Question

Example 1. I have a file test.js

const lib = {
  foo: () => console.log(a)
};
lib.foo(); // can't access "a" before init
const a = 3;

Example 2. I have two files: test1.js and test2.js

const lib = require('./test2');
lib.foo(); // 3

const lib = {
  foo: () => console.log(a) 
};

const a = 3;
module.exports = lib;

Question: Why second example is valid?

Your second example with a module would even be valid if you did module.exports.foo = () => console.log(a); const a = 3; where you export the function before initialising the constant. All that matters is that it's not called before a is initialised. — Bergi
– Bergi, Commented Jul 11, 2022 at 16:09

ᴓᴓᴓ · Accepted Answer · 2022-07-11 16:03:58Z

1

For the same reason this is valid:

const lib = {
  foo: () => console.log(a)
};
const a = 3;
lib.foo();

a exists before export, so it exists when it is called.

answered Jul 11, 2022 at 16:03

ᴓᴓᴓ

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Comments

Christopher Styles · Accepted Answer · 2022-07-11 16:05:58Z

0

in the first case, you are accessing the value of "a" even before you are assigning the value for "a",

in second case, it is declared then it is used, so 2nd case works good and first case gives you error

answered Jul 11, 2022 at 16:05

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