0xD34F

const check = count === [
  count1 + count2,
  count1 - count2,
  count1 * count2,
  count1 / count2,
][Math.random() * 4 | 0];

const check = count === eval(`${count1} ${'+-*/'[Math.floor(Math.random() * 4)]} ${count2}`);

onKeyDown = ({ key }) => {
  this.setState(() => ({
    keyDown: key,
  }));
}

componentDidMount() {
  document.addEventListener('keydown', this.onKeyDown);
}

componentWillUnmount() {
  document.removeEventListener('keydown', this.onKeyDown);
}

<компонент-которому-нужен-id-пользователя v-if="$store.getters.userId">

watch: {
  '$store.getters.userId': {
    immediate: true,
    handler(userId) {
      if (userId) {
        ...
      }
    },
  },
},

array_filter($arr1, fn($n) => in_array($n, $arr2), ARRAY_FILTER_USE_KEY)

<v-data-table
  :item-class="itemClasses"
  ...

methods: {
  itemClasses: item => ({
    red: !(item.id % 3),
  }),
  ...
},

.red {
  background: red;
}

const elements = document.querySelector('#list').children;
// или
const elements = document.querySelectorAll('#list li');

const getVal = el => +el.textContent.split(' - ').pop();
// или
const getVal = el => parseInt(el.innerText.replace(/.*\D/, ''));
// или
const getVal = el => el.innerHTML.match(/\d+$/) | 0;

const sum = Array.prototype.reduce.call(
  elements,
  (acc, n) => acc + getVal(n),
  0
);

// или

let sum = 0;
for (const n of elements) {
  sum += getVal(n);
}

// или

const sum = (function sum(i) {
  return elements[i] ? getVal(elements[i]) + sum(i + 1) : 0;
})(0);

// или

const sum = eval(Array.from(elements, getVal).join('+')) ?? 0;

const digitsOnly = str => str.replace(/\D/g, '');

// или

const digitsOnly = str => (str.match(/\d/g) ?? []).join('');

// или

const digitsOnly = str => ''.concat(...str.matchAll(/\d/g));

// или

const digitsOnly = str => str.split(/\D/).join``;

// или

const digitsOnly = str =>
  Array.prototype.reduce.call(
    str,
    (acc, n) => acc + ('0123456789'.includes(n) ? n : ''),
    ''
  );

document.querySelectorAll('span').forEach(n => {
  n.innerText = digitsOnly(n.innerText);
});

// или

for (const n of document.getElementsByTagName('span')) {
  n.textContent = digitsOnly(n.textContent);
}

if (state) {
  this.x = 'c';
} else if (route) {
  this.x = 'b';
} else if (prop) {
  this.x = 'a';
}

this.x = [
  [ state, 'c' ],
  [ route, 'b' ],
  [  prop, 'a' ],
].find(n => n[0])?.[1] ?? this.x;

this.x = 
  state ? 'c' :
  route ? 'b' :
  prop  ? 'a' :
          this.x;

switch (true) {
  case !!state: this.x = 'c'; break;
  case !!route: this.x = 'b'; break;
  case  !!prop: this.x = 'a'; break;
}

mounted () {
  ...

watch: {
  showModal(val) {
    $(this.$refs.modal).modal(val ? 'show' : 'hide');
  },
},

const type = x => x == null ? x : x.constructor;

type() === undefined // true
type(null) === null // true
type(/./) === RegExp // true
type(666) === Number // true
type(type) === Function // true

const typename = x => x?.constructor.name ?? `${x}`;

typename() // 'undefined'
typename(null) // 'null'
typename(false) // 'Boolean'
typename(187) // 'Number'
typename('hello, world!!') // 'String'
typename(/./) // 'RegExp'
typename({}) // 'Object'
typename([]) // 'Array'
typename(document.body) // 'HTMLBodyElement'
typename(document.getElementsByClassName('xxx')) // 'HTMLCollection'
typename(new class XXX {}) // 'XXX'
typename(typename) // 'Function'

const newArr = arr.reduce((acc, n, i) => (acc.push(n + (acc[i - 1] ?? 0)), acc), []);

// или

const newArr = arr.reduce((acc, n) => (acc[0].push(acc[1] += n), acc), [ [], 0 ])[0];

// или

const newArr = arr.map((n, i, a) => eval(a.slice(0, i + 1).join('+')));

// или

const newArr = arr.map((n, i, a) => a.reduce((acc, m, j) => acc + m * (j <= i), 0));

например на body

methods: {
  onClick() {
    document.body.classList.toggle('active');
  },
},

computed: {
  headerClass() {
    return в зависимости от this.$route;
  },
},

{reviews.map(n => (
  ...
  {Array.isArray(n.children) && n.children.length ? <Reviews reviews={n.children} /> : null}
  ...
))}

methods: {
  onKeyPress(e) {
    if (/* нажато что надо */) {
      this.$refs.searchInput.focus();
    }
  },
},
created() {
  document.addEventListener('keypress', this.onKeyPress);
  this.$on('hook:beforeDestroy', () => document.removeEventListener('keypress', this.onKeyPress));
},