Реализовать функцию addDigits() [закрыт]

function addDigits(x) { 
  let m = x % 9; 
  return x == 0 ? 0 : m == 0 ? 9 : m; 
} 
 
console.log(addDigits(0)); 
console.log(addDigits(9)); 
console.log(addDigits(67)); 
console.log(addDigits(333)); 
console.log(addDigits(111111111)); 
console.log(addDigits(444)); 
console.log(addDigits(1111111111)); 
console.log(addDigits(123456789078));

.as-console-wrapper.as-console-wrapper { max-height: 100vh }

f=x=>x?x%9||9:0 
 
console.log(f(0)); 
console.log(f(9)); 
console.log(f(67)); 
console.log(f(333)); 
console.log(f(111111111)); 
console.log(f(444)); 
console.log(f(1111111111)); 
console.log(f(123456789078));

.as-console-wrapper.as-console-wrapper { max-height: 100vh }

function add(str) { 
  if(typeof str !== 'string') { 
    str = str.toString(); 
  } 
  let res = str.split('').reduce((acc, cur) => { 
    return acc += parseInt(cur); 
  }, 0); 
  if(res.toString().split('').length > 1) { 
  	res = add(res.toString()); 
  } 
  return res; 
} 
 
console.log(add(999)); 
console.log(add(888)); 
console.log(add(88)); 
console.log(add(1));

function sum(x) { 
  while (x > 9) { 
    for (var y=x, x=0; y; y=Math.floor(y/10)) { 
      x += y % 10 
    } 
  } 
   
  return x 
} 
 
console.log(sum(0)) 
console.log(sum(9)) 
console.log(sum(67)) 
console.log(sum(333)) 
console.log(sum(111111111)) 
console.log(sum(444)) 
console.log(sum(1111111111)) 
console.log(sum(123456789078))

.as-console-wrapper.as-console-wrapper { max-height: 100vh }