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JavaScriptIntermediate#objects
JavaScriptIntermediate#es6#modules
What is the difference between a module and a script? (import/export)
ES modules have their own scope, are always strict, load deferred and support static import/export analysis for tree shaking. Classic scripts share the global scope.
Example
// utils.js
export const add = (a,b) => a+b;
export default add;
// app.js
import add, { add as named } from './utils.js';