ESLint error: Unexpected assignment within a 'while' statement

Question

I have a function that formats currency:

export const formatDollar = (dollar) => {
  const format = function moneyFormat(val, sign = '$ ') {
    const pieces = parseFloat(val).toFixed(2).split('');
    let ii = pieces.length - 3;
    while ((ii -= 3) > 0) {
      pieces.splice(ii, 0, ',');
    }
    return sign + pieces.join('');
  };
  return format(dollar);
};

This part is causing an ESLint error:

while ((ii -= 3) > 0) { pieces.splice(ii, 0, ','); }

error Unexpected assignment within a 'while' statement no-cond-assign

How should i write this statement so that ESLint check passes?

Answer 1

Expression ii -= 3 is equivalent to ii = ii - 3 and can be replaced with ii - 3 > 0. However, since in this case it doesn't modify variable ii anymore. You need to decrement it explicitly in loop. So you could rewrite it like this:

while (ii > 3) { // or ii - 3 > 0
  ii = ii - 3;
  pieces.splice(ii, 0, ',');
}

Couple of tests:

const formatDollar = (dollar) => {
  const format = function moneyFormat(val, sign = '$ ') {
    const pieces = parseFloat(val).toFixed(2).split('');
    let ii = pieces.length - 3;
    while (ii > 3) {
      ii = ii - 3
      pieces.splice(ii, 0, ',');
    }
    return sign + pieces.join('');
  };
  return format(dollar);
};

console.log(formatDollar(12345678))
console.log(formatDollar(12345))
console.log(formatDollar(12))
console.log(formatDollar(.12))