Import syntax variations in Typescript

Introduction

Import syntax lets you bring code from other files or libraries into your current file. This helps you reuse code and keep your project organized.

When you want to use a function or variable defined in another file.

When you need to include a whole library or module to use its features.

When you want to import only specific parts of a module to keep your code small.

When you want to rename an imported item to avoid name conflicts.

When you want to import everything from a module under one name.

Syntax

Typescript

import defaultExport from 'module-name';
import * as name from 'module-name';
import { export1, export2 } from 'module-name';
import { export1 as alias1 } from 'module-name';
import defaultExport, { export1, export2 } from 'module-name';
import 'module-name';

Use single quotes or double quotes for module names.

Default export means the main thing exported from a module.

Examples

Imports the default export from the 'react' module, usually the main React object.

Typescript

import React from 'react';

Imports everything from the local 'utils' file as an object named Utils.

Typescript

import * as Utils from './utils';

Imports only the useState and useEffect functions from the 'react' module.

Typescript

import { useState, useEffect } from 'react';

Imports useState but renames it to useLocalState to avoid name conflicts.

Typescript

import { useState as useLocalState } from 'react';

Sample Program

This program imports two functions, sqrt and pow, from the 'mathjs' library. It calculates the square root and the square of a number and prints the results.

Typescript

import { sqrt, pow } from 'mathjs';

const number = 16;
const root = sqrt(number);
const power = pow(number, 2);

console.log(`Square root of ${number} is ${root}`);
console.log(`${number} raised to power 2 is ${power}`);

Important Notes

Always check if the module you want to import from has a default export or named exports.

You can combine default and named imports in one statement.

Importing a module without bindings (import 'module-name';) runs the module code but does not import anything.

Summary

Import syntax helps you bring code from other files or libraries into your file.

You can import default exports, named exports, or everything as an object.

Renaming imports helps avoid name conflicts in your code.

Practice

1. Which import syntax correctly imports the default export from a module named utils?

easy

A. import utils from './utils';

B. import { utils } from './utils';

C. import * as utils from './utils';

D. import utils = require('./utils');

Solution

1. Step 1: Understand default export import syntax

   The default export is imported without curly braces using import name from 'module'.

2. Step 2: Analyze each option

   import utils from './utils'; uses the correct syntax for default import. import { utils } from './utils'; uses curly braces which is for named exports. import * as utils from './utils'; imports everything as an object, not default. import utils = require('./utils'); is CommonJS style, not ES module syntax.

3. Final Answer:

   import utils from './utils'; -> Option A

4. Quick Check:

   Default import = import name from 'module' [OK]

Hint: Default imports have no braces, named imports do [OK]

Common Mistakes:

• Using curly braces for default imports
• Confusing * as import with default import
• Mixing CommonJS require syntax with ES modules

2. Which of the following is the correct syntax to import only the named export calculate from a module mathUtils?

easy

A. import calculate from './mathUtils';

B. import { calculate } from './mathUtils';

C. import * as calculate from './mathUtils';

D. import calculate = require('./mathUtils');

Solution

1. Step 1: Identify named export import syntax

   Named exports are imported using curly braces: import { name } from 'module'.

2. Step 2: Check each option

   import { calculate } from './mathUtils'; correctly imports the named export calculate. import calculate from './mathUtils'; is for default imports. import * as calculate from './mathUtils'; imports all exports as an object, not a single named export. import calculate = require('./mathUtils'); uses CommonJS syntax, not ES modules.

3. Final Answer:

   import { calculate } from './mathUtils'; -> Option B

4. Quick Check:

   Named import = import { name } from 'module' [OK]

Hint: Use curly braces for named imports only [OK]

Common Mistakes:

• Omitting curly braces for named imports
• Using * as import when only one named export is needed
• Confusing default and named import syntax

3. Given the following code, what will be the output?

import * as helpers from './helpers';

console.log(typeof helpers);
console.log(typeof helpers.formatDate);

Assume helpers exports a function named formatDate.

medium

A. "object" and "object"

B. "function" and "undefined"

C. "object" and "function"

D. "undefined" and "function"

Solution

1. Step 1: Understand import * as syntax

   Using import * as helpers imports all exports as an object named helpers.

2. Step 2: Determine types of helpers and helpers.formatDate

   helpers is an object, so typeof helpers is "object". formatDate is a function exported inside helpers, so typeof helpers.formatDate is "function".

3. Final Answer:

   "object" and "function" -> Option C

4. Quick Check:

   import * as = object, function inside = function [OK]

Hint: import * as creates an object with exported members [OK]

Common Mistakes:

• Thinking import * as imports a function directly
• Confusing typeof results for functions and objects
• Assuming default export with import * as syntax

4. Identify the error in this import statement:

import { default as myFunc } from './module';

medium

A. You cannot rename the default import using curly braces.

B. The syntax is correct; no error.

C. You must use import myFunc from './module'; for default imports.

D. Default imports must be imported with * as syntax.

Solution

1. Step 1: Understand default import syntax

   Default imports are imported without curly braces and can be renamed directly: import myFunc from 'module'.

2. Step 2: Analyze the given syntax

   The syntax import { default as myFunc } tries to rename the default export inside curly braces, which is invalid in ES module syntax.

3. Final Answer:

   You cannot rename the default import using curly braces. -> Option A

4. Quick Check:

   Default import no braces, no rename inside braces [OK]

Hint: Default imports never use curly braces [OK]

Common Mistakes:

• Trying to rename default import inside curly braces
• Confusing named export renaming with default import
• Assuming default import can be destructured

5. You want to import a named export parseData from dataUtils but avoid naming conflicts by renaming it to parse. Which is the correct import statement?

hard

A. import parse from './dataUtils';

B. import { parse as parseData } from './dataUtils';

C. import * as parse from './dataUtils';

D. import { parseData as parse } from './dataUtils';

Solution

1. Step 1: Understand renaming named imports

   You can rename named imports using import { originalName as newName }.

2. Step 2: Check each option

   import { parseData as parse } from './dataUtils'; correctly renames parseData to parse. import parse from './dataUtils'; imports default export, not named. import * as parse from './dataUtils'; imports all exports as an object named parse. import { parse as parseData } from './dataUtils'; tries to rename parse to parseData, which is reversed.

3. Final Answer:

   import { parseData as parse } from './dataUtils'; -> Option D

4. Quick Check:

   Rename named import with 'as' inside braces [OK]

Hint: Use 'as' inside braces to rename named imports [OK]

Common Mistakes:

• Using default import syntax for named exports
• Confusing rename direction in 'as' syntax
• Using * as when only one function is needed