JavaScript Stack Overflow Answers

Selected technical solutions from my Stack Overflow history. These cover iteration, Proxies, the event loop, and data transforms — not a vote leaderboard.

for (const [k, v] of collection.entries()) {
    console.log(k, v);
}
for (const { name, views } of collection) {
    console.log(name, views);
}

const fmt = new Intl.DateTimeFormat('en-US', {
    year: 'numeric', day: '2-digit', month: 'short'
});
fmt.formatToParts(date).filter(p => p.type !== 'literal').map(p => p.value).join('/');

console.log(structuredClone(array));
array.push({ fruit: 'apple' });
console.log(structuredClone(array));

const map = new Map();
for (let i = 0; i < foodsList.length; i++) {
    const item = foodsList[i];
    map.has(item.originCode) || map.set(item.originCode, item.foodOrigin);
}
const result = Array.from(map, ([originCode, foodOrigin]) => ({ foodOrigin, originCode }));

const result = Array(arr.length);
for (let i = 0; i < arr.length; i++) {
    const item = result[i] = Array(th.length);
    for (let j = 0; j < th.length; j++) {
        item[j] = arr[i][th[j]];
    }
}

class B extends A {
    constructor() {
        super();
        delete this.foo;
    }
    get foo() {
        return 'baz';
    }
}

const result = [], last = [{ children: result }];
for (const { lv, name } of arr) {
    const node = { name, children: null };
    (last[lv].children ??= []).push(node);
    last[lv + 1] = node;
}

get(t, prop) {
    if (keys.has(prop)) return;
    return Reflect.get(...arguments);
},
has(t, prop) {
    if (keys.has(prop)) return false;
    return Reflect.has(...arguments);
}

// @benchmark shift
2 << 1
// @benchmark multiply
2 * 2

const DAY_TIME = 3600 * 24 * 1000;
const isSameDate = (a, b) => {
    a = a.getTime();
    b = b.getTime();
    return (a - a % DAY_TIME) === (b - b % DAY_TIME);
};

const fileList = fs.readdirSync(dir, { withFileTypes: true });
fileList.forEach(file => file.isDirectory()
    ? getFiles(`${dir}/${file.name}`, files)
    : files.push(`${dir}/${file.name}`));

Object.setPrototypeOf(Function.prototype, prototype);

const mapped = arr.reduce((map, item) => {
    map[item[0]] ??= [];
    item.length > 1 && map[item[0]].push(item);
    return map;
}, {});
const result = Object.entries(mapped).reduce((result, [key, val]) => {
    result.push([key], ...val);
    return result;
}, []);

for (const ch of str) {
    console.log(ch);
}

const worker = new Worker(URL.createObjectURL(blob));
worker.addEventListener('message', e => {
    if ('duration' in e.data) resolve(e.data.duration);
    else progressCb(e.data.progress);
});

const keys = [...map2.keys()];
arr1.forEach(item => keys.forEach(key => (key in item) && (item[key] = map2.get(key))));

({ clone: structuredClone.bind(null) }).clone(1);

const callableObject = new Proxy(new Function, {
    apply() { console.log('invoked'); },
    get(_, prop) { return Reflect.get(obj, prop); },
    set(_, prop, val) { Reflect.set(obj, prop, val); }
});

new MutationObserver(list => {
    console.log('aria-hidden changed');
}).observe($test, { attributeFilter: ['aria-hidden'] });