reverse без использования методов

numbers.reverse = function() {
 
  for (let i = this.length - 1; i >= 0; i--) {
    
    }
  }
};

const a = [36,55,100,39,22,11];
 
for(let i = 0, j = a.length - 1; i < a.length / 2; i++, j--) {
    [a[i], a[j]] = [a[j], a[i]];
}
 
console.log(a); // [11, 22, 39, 100, 55, 36]

for (let i = a.length - 1; i > 0; i -= 1)
  [a[a.length-i],a[i]]=[a[i],a[a.length-i]];

const a = [1, , undefined, 4];
 
console.log(a); // [ 1, <1 empty slot>, undefined, 4 ]
 
for (let i = 0, j = a.length - 1; i < a.length / 2; i++, j--) {
  [a[i], a[j]] = [a[j], a[i]];
}
console.log(a); // [ 4, undefined, undefined, 1 ]
 
const b = [1, , undefined, 4];
 
const newArr = [];
b.forEach((value, key) => {
  newArr[b.length - key - 1] = value;
});
 
console.log(newArr); // [ 4, undefined, <1 empty slot>, 1 ]
 
console.log(b.reverse()); // [ 4, undefined, <1 empty slot>, 1 ]

const a = [1, , undefined, 'viva la siski!'];
typeof a[1]; // undefined
typeof a[2]; // undefined

const a = [36, 55, 100, 39, 22, 11];
 
for (let i = a.length - 1; i > 0; i -= 1)
    [a[a.length-i],a[i]]=[a[i],a[a.length-i]];
 
console.log(a); // [36, 55, 100, 39, 22, 11]

for (let i = a.length - 1; i >= a.length / 2; i -= 1)
    [a[a.length-1-i],a[i]]=[a[i],a[a.length-1-i]];
 
console.log(a); // [[11, 22, 39, 100, 55, 36]]

function isEmptySlot(arr, index) {
  let f = true;
  a.slice(index, index + 1).forEach((_) => (f = false));
  return f;
}

const flip1 = a => {
  let res = [];
  for (let i = 0; i < a.length; i += 1)
    res = [a[i], ...res];
  return res;
}
 
const flip2 = a => {
  let [i, sz] = [0, a.length];
  while (sz) {
    a = [a[i], ...a];
    [i, sz] = [i + 2, sz - 1];
  }
  a.length = (i / 2);
  return a;
}

const a = [1, , 3, 4]; //  [ 1, <1 empty slot>, 3, 4 ]
 
const sl = a.length;
a.length = a.length * 2;
for (const n in a) {
  if (n > sl) {
    break;
  }
  a[a.length - n - 1] = a[n];
}
 
for (let i = 0; i < sl; i++) {
  a.shift();
}
 
console.log(a); // [ 4, 3, <1 empty slot>, 1 ]