Karatasi ya Maelezo ya JavaScript
Rejeleo linalotafutika na linaloweza kuchapishwa la JavaScript ya kisasa — sintaksia, safu, mifuatano, vitu, async/await, DOM na vipengele vya ES2022+. Bila malipo.
Variables & types
10let x = 1;
Block-scoped, reassignable variable
const PI = 3.14;
Block-scoped constant binding
typeof value
Returns the type as a string
Number('42')
Convert a string to a number
String(42)
Convert a value to a string
parseInt('42px', 10)
Parse a leading integer (base 10)
Boolean(0)
Coerce a value to true/false
value ?? 'default'
Nullish coalescing (null/undefined only)
a?.b?.c
Optional chaining, short-circuits on null
Array.isArray(x)
Check whether a value is an array
Functions
9function add(a, b) { return a + b; }
Named function declaration
const add = (a, b) => a + b;
Arrow function with implicit return
const f = (a = 1) => a;
Default parameter value
function f(...args) {}
Rest parameters collect into an array
f(...arr)
Spread an array into arguments
const { a, b } = obj;
Object destructuring
const [x, y] = arr;
Array destructuring
(function(){})()
Immediately-invoked function (IIFE)
fn.bind(this)
Bind a fixed this context
Strings
10`Hello ${name}`
Template literal interpolation
str.length
Number of characters
str.includes('a')
Check if a substring exists
str.slice(0, 3)
Extract part of a string
str.replace(/a/g, 'b')
Replace matches (regex)
str.split(',')
Split into an array
str.trim()
Remove surrounding whitespace
str.toUpperCase()
Convert to upper case
str.padStart(3, '0')
Pad the start to a length
str.at(-1)
Character at index (supports negatives)
Arrays
11arr.map(x => x * 2)
Transform each element
arr.filter(x => x > 0)
Keep matching elements
arr.reduce((a, b) => a + b, 0)
Reduce to a single value
arr.find(x => x.id === 1)
First matching element
arr.some(x => x > 0)
True if any element matches
arr.every(x => x > 0)
True if all elements match
arr.includes(3)
Check for a value
arr.sort((a, b) => a - b)
Numeric ascending sort
[...new Set(arr)]
Remove duplicate values
arr.flat(Infinity)
Fully flatten nested arrays
arr.at(-1)
Last element (negative index)
Objects
9Object.keys(obj)
Array of own enumerable keys
Object.values(obj)
Array of own values
Object.entries(obj)
Array of [key, value] pairs
{ ...a, ...b }
Merge objects (spread)
Object.assign({}, a, b)
Copy/merge into a target
Object.freeze(obj)
Make an object immutable
{ [key]: value }
Computed property name
obj.hasOwnProperty('x')
Check for an own property
structuredClone(obj)
Deep clone an object
Async & promises
9async function f() {}
Declare an async function
await fetch(url)
Pause until a promise resolves
Promise.all([p1, p2])
Wait for all to resolve
Promise.allSettled([p1, p2])
Wait for all to settle
Promise.race([p1, p2])
Resolve with the first to settle
new Promise((res, rej) => {})
Create a promise manually
try { await f(); } catch (e) {}
Handle async errors
setTimeout(fn, 1000)
Run after a delay (ms)
queueMicrotask(fn)
Schedule a microtask
Control flow
9if (a) {} else if (b) {} else {}
Conditional branches
a ? b : c
Ternary expression
switch (x) { case 1: break; }
Multi-way branch
for (const x of arr) {}
Iterate values (iterables)
for (const k in obj) {}
Iterate object keys
while (cond) {}
Loop while a condition holds
arr.forEach((x, i) => {})
Run a callback per element
break / continue
Exit or skip a loop iteration
label: for (...) { break label; }
Break out of nested loops
DOM & events
10document.querySelector('.x')
First matching element
document.querySelectorAll('.x')
All matching elements (NodeList)
el.addEventListener('click', fn)
Attach an event listener
el.classList.toggle('active')
Toggle a CSS class
el.dataset.id
Read a data-id attribute
el.textContent = 'hi'
Set text safely (no HTML)
el.setAttribute('aria-hidden', true)
Set an attribute
e.preventDefault()
Cancel the default action
el.closest('.parent')
Nearest matching ancestor
document.createElement('div')
Create a new element
Classes & modules
9class A extends B {}
Class with inheritance
constructor() { super(); }
Initialize and call the parent
#private = 1;
Private class field
static create() {}
Static method on the class
get value() {}
Getter accessor
export default fn;
Default module export
export { a, b };
Named module exports
import x, { y } from './m.js'
Default + named imports
const m = await import('./m.js')
Dynamic import
Hakuna kipengele kinacholingana na “:q”.
Kuhusu Karatasi ya Maelezo ya JavaScript
Karatasi hii ya kumbukumbu ya JavaScript ni rejea inayoweza kutafutwa, ya ukurasa mmoja, kwa lugha ya kisasa: variables na aina, functions, strings, arrays, objects, async na promises, control flow, DOM na events, na classes na modules. Kila kipengele huoanisha snippet halisi ya msimbo na maelezo ya mstari mmoja kuhusu inavyofanya.
Imeandikwa kwa JavaScript ambayo watu hutumia kwa uhalisia leo — let na const, arrow functions, destructuring, spread, optional chaining, template literals, async/await na ES modules — hivyo hufanya kazi pia kama ukumbusho wa haraka unaporudi kutoka lugha nyingine.
Karatasi nzima hupakiwa upande wa mteja na ni bure. Ichuje papo hapo kwa kisanduku cha utafutaji, ruka kati ya sehemu kutoka orodha ya yaliyomo inayoning'inia (sticky), bofya snippet yoyote kuinakili, na chapisha ukurasa kwa rejea ya JavaScript ya mezani.
Jinsi ya kutumia Karatasi ya Maelezo ya JavaScript
- Fungua karatasi na pitia orodha ya sehemu — kutoka Variables & types kupitia DOM & events hadi Classes & modules.
- Andika kwenye kisanduku cha utafutaji kuchuja kila mstari papo hapo; kihesabu cha ulinganifu huonyesha snippets ngapi zinalingana.
- Tumia orodha ya yaliyomo inayoning'inia kuruka moja kwa moja kwenye sehemu kama Async & promises.
- Bofya snippet, au ikoni yake ya kunakili, kunakili msimbo kwenye clipboard yako.
- Bofya Print kwa nakala safi, inayofaa kuchapishwa, ya rejea nzima.
Maswali yanayoulizwa mara kwa mara
Sehemu tisa: variables na aina, functions, strings, arrays, objects, async na promises, control flow, DOM na events, na classes na modules — kila moja kama snippets tayari kunakiliwa zenye maelezo mafupi.
Ndiyo. Snippets hutumia sintaksia ya sasa — let/const, arrow functions, destructuring, optional chaining, async/await, classes na ES modules — ikionyesha JavaScript ya ES2022+ badala ya mifumo ya zamani.
Ndiyo. Kubofya snippet yoyote ya msimbo, au ikoni ya kunakili inayotokea unapopitisha mshale juu ya mstari, huiweka kwenye clipboard yako mara moja pamoja na uthibitisho mfupi wa "Copied!".
Ndiyo. Kitufe cha Print hutoa mpangilio safi bila upau wa utafutaji, urambazaji na vitufe, hivyo kurasa zilizochapishwa huwa na snippets na maelezo yake tu.
Ndiyo. Ni bure, hupakia kabisa kwenye kivinjari chako, na haihitaji akaunti.
Utafutaji maarufu
javascript cheat sheet
js cheat sheet
javascript array methods
javascript string methods
javascript promises and async await
javascript object methods
js dom methods
javascript syntax reference
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