JavaScript中保留小数点后N位方法总结

(1).toFixed(2) // '1.00'
(1.2).toFixed(2) // '1.20'
(-2).toFixed(2) // '-2.00'
(1.12345678).toFixed(7) // '1.1234568'

(1111111111.1234567891234).toFixed(8) // '1111111111.12345672'

function roundFun(number, precision) {
  return Math.round(+number + 'e' + precision) / Math.pow(10, precision);
}
// 或
function roundFun(number, precision) {
  return Math.round(number * Math.pow(10, precision)) / Math.pow(10, precision);
}

roundFun(1, 2) // 1
roundFun(1.2, 2) // 1.2
roundFun(-2, 2) // -2
roundFun(1.12345678, 7) // 1.1234568
roundFun(1111111111.1234567891234, 8) // 1111111111.1234567

const keepDecimal = (numStr, precision) => {
  const regexp = new RegExp(`^\\d+(?:\\.\\d{0,${precision}})?`)
  const result = numStr.match(regexp)
  return result ? result[0] : '0'
}

keepDecimal('1', 2) // '1'
keepDecimal('1.2', 2) // '1.2'
keepDecimal('1.12345678', 7) // '1.1234567'
keepDecimal('12345.1234567891234', 8) // '12345.12345678'
keepDecimal('123456789.1234567891234', 10) // '123456789.1234567891'

keepDecimal('-2', 2) // '0'
keepDecimal('122sss', 10) // '122'
keepDecimal('abcd', 10) // '0'

const keepDecimal = (numStr, precision) => {
  const regexp = new RegExp(`^\\d+(?:\\.\\d{0,${precision}})?`)
  const result = numStr.match(regexp)
  return result ? result[0] : '0'
}

const keepDecimalPlaces = (numStr, precision) => {
  let numberStr = keepDecimal(numStr, precision)
  let rs = numberStr.indexOf('.')
  if (rs < 0 && precision > 0) {
    rs = numberStr.length
    numberStr += '.'
  }
  while (numberStr.length <= rs + precision) {
    numberStr += '0'
  }
  return numberStr
}

keepDecimalPlaces('1', 2) // '1.00'
keepDecimalPlaces('1.2', 2) // '1.20'
keepDecimalPlaces('1.12345678', 7) // '1.1234567'
keepDecimalPlaces('12345.1234567891234', 8) // '12345.12345678'
keepDecimalPlaces('123456789.1234567891234', 10) // '123456789.1234567891'
keepDecimalPlaces('123456789.000001', 10) // '123456789.0000010000'

keepDecimalPlaces('-2', 2) // '0.00'
keepDecimalPlaces('122sss', 10) // '122.0000000000'
keepDecimalPlaces('abcd', 10) // '0.0000000000'