Built-ins
Quickly see the shape of a built-in — its properties, methods, and what you can do with it.
| Built-in | What it covers |
|---|---|
| Array | Mutating vs non-mutating methods, transforms, iteration |
| Date | Constructors, formatting, arithmetic, gotchas |
| Error | Properties, built-in types, custom errors, cause chaining |
| Event | Properties, bubbling, delegation, custom events |
| .filter() | Syntax, common patterns, edge cases |
| for | for, for…of, for…in, labeled loops |
| .forEach() | Syntax, gotchas, when to use map instead |
| FormData | Reading forms, appending, sending with fetch |
| Object.fromEntries() | Converting arrays/maps to objects |
| .map() | Syntax, transforms, index usage |
| Object | Keys, values, entries, assign, freeze, spread |
| .reduce() | Accumulator patterns, when to avoid |
| RegExp | Patterns, flags, methods, common recipes |
| Set | Creation, methods, ES2025 set operations |
| typeof | Type checking, quirks, alternatives |
| while | while, do…while, break, continue |
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