JavaScript Modules
Modules allow you to break large codebases into independent, reusable files.
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📋 Copy ES Modules Export and Import Cheat Sheet
// ES Modules (ESM) Standard Syntax
// math.js:
export const PI = 3.14159;
export function add(a, b) { return a + b; }
export default class Calculator {}
// app.js:
import Calculator, { PI, add } from "./math.js";⚠️ 5 Fatal Traps & JavaScript Pitfalls
Trap #1: Missing File Extension in Browser ESM
In standard browser ES modules, writing
import { add } from "./math" fails with a 404 error. Browsers require the full file extension: "./math.js".Trap #2: CommonJS vs. ES Module Interop Confusion
Mixing
require() and import statements in the same file causes syntax errors. Configure "type": "module" in package.json to standardize on ESM.Trap #3: Default Export Renaming Confusion
Default exports can be imported under any arbitrary name, which can lead to inconsistent naming across team files. Prefer named exports for refactoring clarity.
Trap #4: Dynamic import() Returns a Promise
import(modulePath) is asynchronous and returns a Promise. Forgetting to await import(...) leaves you with a pending promise instead of module exports.Trap #5: Top-Level Await Blocking Module Tree Execution
Using top-level
await in an imported module pauses the execution of all parent importing modules until the promise resolves.💬 Frequently Asked Questions
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