JavaScript Cheat Sheet
Essential JavaScript concepts, ES6+ features, and common methods.
3 PagesBeginnerMay 18, 2026
Variables
Three ways to declare variables.
javascript
const name = "SkillVeris"; // Cannot reassignlet count = 0; // Can reassignvar old = "legacy"; // Avoid (function-scoped)
Data Types
JavaScript has 8 primitive types.
- string- Text values
- number- Integers and floats
- boolean- true or false
- null- Intentional empty value
- undefined- Uninitialized variable
- object- Key-value collection
- array- Ordered list
- symbol- Unique identifier
Array Methods
Common ES6 array manipulation.
javascript
const nums = [1, 2, 3, 4, 5];const doubled = nums.map(n => n * 2);const evens = nums.filter(n => n % 2 === 0);const sum = nums.reduce((a, b) => a + b, 0);const found = nums.find(n => n > 3); // 4
Promises & Async
Handle asynchronous operations.
javascript
// Async/Awaitasync function fetchData(url) { try { const res = await fetch(url); const data = await res.json(); return data; } catch (err) { console.error(err); }}
Pro Tip
Prefer const over let and let over var. Use optional chaining (?.) to safely access nested properties.
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