WbICHA

type CreatureBasis = {
    People: {
        child: {
            age: number;
            school: string;
        };
        adult: {
            age: number;
            height: number;
            weight: number;
        };
    };
    Animal: {
        fish: {
            waterBody: string;
        };
        cat: {
            catchMouses: boolean;
        };
    };
};
type Creature = {
    [K0 in keyof CreatureBasis]: {
        [K1 in keyof CreatureBasis[K0]]: {
            type: K0;
            subtype: K1;
            params: CreatureBasis[K0][K1];
        };
    }[keyof CreatureBasis[K0]];
}[keyof CreatureBasis];

const obj = {
  val: 1,
  valueOf() {
    return this.val ^= 1;
  },
};

// или

const obj = {
  val: '1',
  toString() {
    return this.val = '1'.slice(this.val.length);
  },
};

// или

const obj = {
  val: true,
  [Symbol.toPrimitive]() {
    return this.val = !this.val;
  },
};

console.log(obj == false, obj == true); // true true
console.log(...Array.from({ length: 5 }, () => +obj)); // 0 1 0 1 0

Array.from(str, n => n < 5 ? 0 : 1).join('')

// или

[...str].reduce((acc, n) => acc + +(n >= 5), '')

// или

''.concat(...str.split('').map(n => Math.floor(n / 5)))

// или

[].map.call(str, n => -~-~-~n >> 3).join``

// или

str.replace(/./g, m => Number('56789'.includes(m)))

// или

str.replace(/[1-4]/g, 0).replace(/[5-9]/g, 1)

будет ли работодатель рассматривать на позицию миддл бек бывшего миддла фронтендщика ?

function round45(value) {
  return Math.round(value / 45) * 45;
}
round45(90.3222341); // 90
round45(136.99); // 135
round45(358); // 360
round45(46); // 45

let b = [1, 2, 3, 0, 4, 5, 6];


const sum = b.slice(0, b.findIndex(e => e === 0)).reduce((total, amount) => total + amount); 

console.log(sum)

const arrToSinglyLinkedList = (arr, nextKey = 'next') =>
  arr.reduceRight((acc, n) => ({ ...n, [nextKey]: acc }), null);

// или

function arrToSinglyLinkedList(arr, nextKey = 'next') {
  let list = null;

  for (let i = arr.length; i--;) {
    const node = Object.assign({}, arr[i]);
    node[nextKey] = list;
    list = node;
  }

  return list;
}

const arrToSinglyLinkedList = (arr, nextKey = 'next', i = 0) =>
  i < arr.length
    ? Object.fromEntries([
        ...Object.entries(arr[i]),
        [ nextKey, arrToSinglyLinkedList(arr, nextKey, -~i) ]
      ])
    : null;

// или

function arrToSinglyLinkedList(arr, nextKey = 'next', i = 0, n = arr[i]) {
  const node = n ? {} : null;
  if (node) {
    for (const k in n) {
      if (n.hasOwnProperty(k)) {
        node[k] = n[k];
      }
    }
    node[nextKey] = arrToSinglyLinkedList(arr, nextKey, i + 1);
  }

  return node;
}

mainArr.reduce((acc, cur) => {
    if (!acc[cur]) acc[cur] = 0;
    acc[cur]++;
    return acc;
}, {})