ES Modules import and export in Node.js - Step-by-Step Execution

Concept Flow - ES Modules import and export

Create module file

↓

Export variables/functions

↓

Create main file

↓

Import exported items

↓

Use imported items

↓

Run program and see output

This flow shows how you create a module with exports, then import those exports in another file to use them.

Execution Sample

Node.js

export const greeting = 'Hello';
export function sayHi(name) {
  return `${greeting}, ${name}!`;
}

import { greeting, sayHi } from './module.js';
console.log(sayHi('Alice'));

Exports a constant and a function from one file, imports them in another, then calls the function to print a greeting.

Execution Table

Step	Action	Evaluation	Result
1	Export const greeting	greeting = 'Hello'	greeting available to import
2	Export function sayHi	sayHi is a function	sayHi available to import
3	Import greeting and sayHi	Imported greeting = 'Hello', sayHi function	Imported items ready to use
4	Call sayHi('Alice')	sayHi('Alice') returns 'Hello, Alice!'	Output string ready
5	console.log output	Prints 'Hello, Alice!'	User sees: Hello, Alice!

💡 Program ends after printing the greeting message.

Variable Tracker

Variable	Start	After Export	After Import	After Function Call	Final
greeting	undefined	'Hello'	'Hello'	'Hello'	'Hello'
sayHi	undefined	function	function	function	function
result	undefined	undefined	undefined	'Hello, Alice!'	'Hello, Alice!'

Key Moments - 3 Insights

Why do we use curly braces {} when importing?

Curly braces are used to import named exports exactly as they were exported. See execution_table step 3 where greeting and sayHi are imported by name.

Can we import without exporting first?

No, you must export variables or functions in the module file before importing them. Step 1 and 2 show exports happen before import in step 3.

What happens if we call sayHi before importing it?

You get an error because sayHi is undefined until imported. The variable_tracker shows sayHi is undefined at start and only defined after import.

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of greeting after import?

A null

B undefined

C 'Hello'

D 'Hi'

💡 Hint

Check execution_table step 3 under Evaluation column.

At which step does the program print the greeting message?

A Step 3

B Step 5

C Step 4

D Step 2

💡 Hint

Look for console.log output in execution_table.

If we remove the export keyword from greeting, what happens when importing?

A Import fails because greeting is not exported

B Import still works normally

C greeting imports as undefined but no error

D Program prints 'Hello' anyway

💡 Hint

Refer to key_moments about needing export before import.

Concept Snapshot

ES Modules let you share code between files.
Use 'export' to share variables or functions.
Use 'import {name}' to bring them in.
Curly braces import named exports.
Run Node.js with --experimental-modules or .mjs extension.
This keeps code organized and reusable.

Full Transcript

This lesson shows how ES Modules work in Node.js. First, you create a module file where you export variables or functions using the export keyword. Then, in another file, you import those exports using import with curly braces around the names. After importing, you can use the imported items like normal variables or functions. The example exports a greeting string and a sayHi function, then imports and calls sayHi to print a greeting message. The execution table traces each step from exporting, importing, calling the function, to printing the output. The variable tracker shows how variables change from undefined to defined after export and import. Key moments clarify why curly braces are needed, why export must come before import, and what happens if you call a function before importing it. The visual quiz tests understanding of variable values after import, when output happens, and the importance of export. The snapshot summarizes the syntax and purpose of ES Modules in Node.js.