Javascript-toFixed（）0.5问题

Question

I have a case where I want to round decimal number by 2 decimal places. For now .toFixed(2) is working fine, however for 0.455 I want to get 0.45 and not 0.46

Is there any quick solution for this? I can use Lodash if it can solve this.

For example I want the followings.

0.455 > 0.45

0.456 > 0.46

0.4549 > 0.45

Answer 1

Multiply by 100, round down with floor, divide with 100, format with toFixed.

function roundDownToFixed2(v) {
  return (Math.floor(v * 100) / 100).toFixed(2);
}
> roundDownToFixed2(0.455)
'0.45'

A more generic version would be

function roundDownToFixed(v, d=2) {
  const mul = Math.pow(10, d);
  return (Math.floor(v * mul) / mul).toFixed(d);
}
> roundDownToFixed(0.455, 2)
'0.45'
> roundDownToFixed(0.4555, 3)
'0.455'

Answer 2

this should help:

function roundDecimal(a, k) {
  let K = Math.pow(10, k);
  return Math.round(a * K) / K;
}

so roundDecimal(0.455, 2) would be 0.46