JavaScript Cheat Sheet

Updated 2026-02-28

JavaScript is a dynamic, prototype-based programming language standardized as ECMAScript and used across browsers, servers (Node.js), and embedded runtimes. This cheat sheet focuses on the most-used language constructs, standard library APIs, and core Web/Node primitives you’ll encounter in real projects. Examples are intentionally minimal and runnable, emphasizing correct modern syntax (ES2015+), predictable semantics, and common pitfalls. Use the links in the first column as the “source of truth” for behavior, edge cases, and compatibility.

What This Cheat Sheet Covers

This topic spans 15 focused tables and 135 indexed concepts. Below is a complete table-by-table outline of this topic, spanning foundational concepts through advanced details.

Table 1: Core Types & EqualityTable 2: Declarations, Scope, and GlobalsTable 3: Functions and thisTable 4: Objects, Prototypes, and ClassesTable 5: Arrays, Sets, and MapsTable 6: Iteration, Iterables, and GeneratorsTable 7: Strings and Regular ExpressionsTable 8: Control Flow, Operators, and ErrorsTable 9: Promises and AsyncTable 10: Modules and LoadingTable 11: Fetch and HTTP Primitives (Web)Table 12: DOM Events and Storage (Web)Table 13: Workers, Service Workers, and CachingTable 14: Node.js Runtime and I/OTable 15: Metaprogramming and Advanced Built-ins

Table 1: Core Types & Equality

Concept	Example	Description
Number	`Number.isFinite(42)`	IEEE-754 floating-point
BigInt	`9007199254740993n + 1n`	Arbitrary-size integers
String	`'a'.toUpperCase()`	UTF-16 code units
Boolean	`Boolean('')`	`true`/`false` values
Symbol	`const k = Symbol('id')`	Unique identifiers

Back to Programming Languages

Updated 2026-02-28

Next Topic: JSON Cheat Sheet

What This Cheat Sheet Covers

This topic spans 15 focused tables and 135 indexed concepts. Below is a complete table-by-table outline of this topic, spanning foundational concepts through advanced details.

Table 1: Core Types & Equality

Concept	Example	Description
Number	`Number.isFinite(42)`	IEEE-754 floating-point
BigInt	`9007199254740993n + 1n`	Arbitrary-size integers
String	`'a'.toUpperCase()`	UTF-16 code units
Boolean	`Boolean('')`	`true`/`false` values
Symbol	`const k = Symbol('id')`	Unique identifiers