JavaScript Cheat Sheet

Core JavaScript syntax, array methods, and DOM manipulation.

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Types & Vars Array Tools Object Tricks Promises & Fetch Modern Syntax Event Handling
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Types & Vars

Concept / Tag Code Snippet Description
Type Check 
typeof variable === "string"
 Verify data type.
Null Coalescing 
const name = user.name ?? "Guest";
 Fallback for null/undefined.

Array Tools

Concept / Tag Code Snippet Description
Filter 
const young = users.filter(u => u.age < 18);
 New array with matches.
Reduce Sum 
const sum = orders.reduce((s, o) => s + o.price, 0);
 Condense array to total.
Some/Every 
arr.some(x => x > 0) | arr.every(...)
 Boolean checks.

Object Tricks

Concept / Tag Code Snippet Description
Merge Objects 
const combined = { ...obj1, ...obj2 };
 Shallow merge clones.
Optional Chain 
user?.profile?.bio
 Safe nested access.

Promises & Fetch

Concept / Tag Code Snippet Description
Post Request 
fetch(url, { method: "POST", body: JSON.stringify(data) });
 Send data to API.
Async/Await 
const data = await promise;
 Handle async synchronous style.

Modern Syntax

Concept / Tag Code Snippet Description
Template String 
`Hello ${username}`
 Interpolated strings.

Event Handling

Concept / Tag Code Snippet Description
Delegate 
parent.addEventListener("click", (e) => { ... });
 Single handler for children.

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