为什么将Math.round输入说乘以1000，然后将结果相除？

Question

A function to convert from temperatures is written below

function tryConvert(temperature, convert /*callback*/) {
  const input = parseFloat(temperature);
  if (Number.isNaN(input)) {
    return '';
  }
  const output = convert(input);
  const rounded = Math.round(output * 1000) / 1000;
  return rounded.toString();
}

My question is this line:

  const rounded = Math.round(output * 1000) / 1000;

Why the need to multiply by 1000? and also divide result by 1000?

Answer 1

Multiplying by 1000 moves the decimal point 3 digits to the right. 5.333333 = > 5333.333

Rounding rounds to whole integers. (Only zeros after decimal point) 5333.333 = > 5333.000

After that dividing by 1000 moves the decimal point back to where it started. 5333.000 = > 5.333000

The result is, that the number is rounded to 3 digits after the decimal point. 5.333333 = > 5.333000

Answer 2

Is to round up the output to 3 decimals:

Example:

 const rounded = Math.round(1.23456 * 1000) / 1000; // = 1.235 console.log(rounded);