Modern JavaScript Core

When to use this skill

• Writing vanilla JavaScript logic.
• Understanding modern syntax in PR reviews.
• Avoiding legacy patterns (var, callbacks).

1. Essential Syntax

• Variables: const by default, let if reassignment is needed. Never var.
• Functions: Arrow functions () => {} for callbacks and lexical this.
• Destructuring: Use generously (const { id, name } = user).
• Template Literals: Use backticks for string interpolation.

2. Async Patterns

• Async/Await: Prefer over .then() chains.
• Top-level Await: Supported in modern modules.
• Promise.allSettled: Better for unrelated concurrent tasks than Promise.all (which fails fast).

3. Modules

• ES Modules: import/export syntax is standard.
• Named Exports: Prefer named exports (export const foo) over export default for better refactoring support.

4. Modern Array Methods

• Usage: map, filter, reduce, find, some, every.
• Newer: floated (toSorted), toSpliced (immutable alternatives).