JA @js_test
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var a = ( function a() {
return '1';
},
function b() {
return 2;
})()
alert(typeof a)const target = { a: 1, b: 2 };
const handler = {
get(obj, prop) {
return prop in obj ? obj[prop] * 2 : 'not found';
},
set(obj, prop, value) {
if (typeof value !== 'number') {
return false;
}
obj[prop] = value + 10;
return true;
}
};
const proxy = new Proxy(target, handler);
proxy.c = '5';
proxy.d = 5;
console.log(JSON.stringify({
a: proxy.a,
b: proxy.b,
c: proxy.c,
d: target.d,
hasC: Reflect.has(target, 'c')
}));const asyncFunction = async () => {
const delay = (ms) => new Promise(resolve => setTimeout(resolve, ms));
const result = await Promise.race([delay(100), delay(500)]);
return result;
};
asyncFunction().then(value => console.log(value));const wMap = new WeakMap();
function foo() {
wMap.set(this, 1);
};
const bar = () => wMap.set(this, 2);
bar();
foo();
console.log(wMap.get(this));
const team = {
lead: { name: 'Alice', projects: ['Alpha', 'Beta'] },
dev: { name: 'Bob', projects: ['Gamma'] },
tester: { name: 'Charlie', projects: [] }
};
const {
lead: { projects: [leadProject] },
dev: { projects: [devProject = 'Delta'] },
tester: { projects: [testerProject = 'Epsilon'] }
} = team;
console.log(`${leadProject}-${devProject}-${testerProject}`);const obj = {};
Object.defineProperty(obj, 'name', {
value: 'Alice',
writable: false,
configurable: false
});
try {
obj.name = 'Bob';
delete obj.name;
console.log(obj.name);
} catch (e) {
console.log('Error:', e.message);
}class ShoppingCart {
constructor() {
if (ShoppingCart.instance) {
return ShoppingCart.instance;
}
this.items = [];
ShoppingCart.instance = this;
}
addItem(item) {
this.items.push(item);
}
getItems() {
return [...this.items];
}
}
const cart1 = new ShoppingCart();
const cart2 = new ShoppingCart();
cart1.addItem('Book');
cart2.addItem('Laptop');
console.log(cart1.getItems());The Экономист ⚡️Дарим сразу три новеньких iPhone 16 за подписку! Для участия в розыгрыше нужно: 1. Быть подписанным на The Экономист, Доллар по тридцать и Чё по трендам? 2. Нажать «Участвую!» под этим постом Бот случайным образом выберет победителей 2 июня в 18:00. Айфоны…
var arr=[1,2,3,4,5];
console.log(arr.map((prev,curr)=>prev+curr));
console.log(arr.reduce((a,b)=>a+b));
console.log(arr.filter((a,b)=> (a + b) <= 5));
const promise = new Promise((resolve, reject) => {
setTimeout(() => resolve(3), 1000);
});
promise
.then(result => {
console.log(result);
return result * 2;
})
.then(result => {
console.log(result);
return new Promise(resolve => setTimeout(() => resolve(result * 3), 1000));
})
.then(result => {
console.log(result);
});const users = [
{ id: 1, name: 'Alice' },
{ id: 2, name: 'Bob' },
{ id: 3, name: 'Charlie' }
];
const userScores = new WeakMap();
// Set scores for users
userScores.set(users[0], 95);
userScores.set(users[1], 80);
// Remove reference to Bob
users[1] = null;
let sum = 0;
for (const user of users) {
if (user && userScores.has(user)) {
sum += userScores.get(user);
}
}
console.log(sum);
function Animal() {}
function Dog() {}
Dog.prototype = Object.create(Animal.prototype);
const rover = new Dog();
console.log(rover.constructor === Animal);let obj = { a: 1 };
Object.freeze(obj);
console.log(Object.isFrozen(obj));
console.log(obj.a = 2);
console.log(obj.a);function* counter() {
let i = 1;
while (true) {
const reset = yield i++;
if (reset) {
i = 1;
}
}
}
const gen = counter();
console.log(gen.next().value);
console.log(gen.next().value);
console.log(gen.next(true).value);
console.log(gen.next().value);const createAsyncFunction = (ms, result) => async () => {
await new Promise(resolve => setTimeout(resolve, ms));
return result;
18
[
createAsyncFunction(1000, "A"),
const asyncFunctions
(
createAsyncFunction(500, "B"),
createAsyncFunction(2000, "C"),
Ig
Promise. race(asyncFunctions.map( func =>
func())).then(result => console.log(result));try {
try {
// Creating a custom error type
class CustomError extends Error {
constructor(message) {
super(message);
this.name = "CustomError";
}
}
const fn = () => {
throw new CustomError("Something went wrong");
};
try {
fn();
} catch (e) {
throw new TypeError("Type error occurred");
}
} catch (e) {
console.log(e instanceof Error, e.name, e instanceof TypeError);
}
} catch (e) {
console.log("Outer catch", e.message);
}var foo = {};
var bar = Object.create(foo);
foo.a = 1;
console.log(bar.a);function Person() {}
var person = new Person();
console.log(person instanceof Person);
console.log(person instanceof Object);function compose(...funcs) {
return function(x) {
return funcs.reduceRight((acc, fn) => fn(acc), x);
};
}
const add10 = x => x + 10;
const multiply2 = x => x * 2;
const toString = x => `Result: ${x}`;
const composed = compose(toString, multiply2, add10);
console.log(composed(5));