综合前面所有答案的知识，

这就是我想到的解决办法:

function toFixedWithoutRounding(num, fractionDigits) {
  if ((num > 0 && num < 0.000001) || (num < 0 && num > -0.000001)) {
    // HACK: below this js starts to turn numbers into exponential form like 1e-7.
    // This gives wrong results so we are just changing the original number to 0 here
    // as we don't need such small numbers anyway.
    num = 0;
  }
  const re = new RegExp('^-?\\d+(?:\.\\d{0,' + (fractionDigits || -1) + '})?');
  return Number(num.toString().match(re)[0]).toFixed(fractionDigits);
}

我的解决方案在typescript(可以很容易地移植到JS):

/**
 * Returns the price with correct precision as a string
 *
 * @param   price The price in decimal to be formatted.
 * @param   decimalPlaces The number of decimal places to use
 * @return  string The price in Decimal formatting.
 */
type toDecimal = (price: number, decimalPlaces?: number) => string;
const toDecimalOdds: toDecimal = (
  price: number,
  decimalPlaces: number = 2,
): string => {
  const priceString: string = price.toString();
  const pointIndex: number = priceString.indexOf('.');

  // Return the integer part if decimalPlaces is 0
  if (decimalPlaces === 0) {
    return priceString.substr(0, pointIndex);
  }

  // Return value with 0s appended after decimal if the price is an integer
  if (pointIndex === -1) {
    const padZeroString: string = '0'.repeat(decimalPlaces);

    return `${priceString}.${padZeroString}`;
  }

  // If numbers after decimal are less than decimalPlaces, append with 0s
  const padZeroLen: number = priceString.length - pointIndex - 1;
  if (padZeroLen > 0 && padZeroLen < decimalPlaces) {
    const padZeroString: string = '0'.repeat(padZeroLen);

    return `${priceString}${padZeroString}`;
  }

  return priceString.substr(0, pointIndex + decimalPlaces + 1);
};

测试用例:

  expect(filters.toDecimalOdds(3.14159)).toBe('3.14');
  expect(filters.toDecimalOdds(3.14159, 2)).toBe('3.14');
  expect(filters.toDecimalOdds(3.14159, 0)).toBe('3');
  expect(filters.toDecimalOdds(3.14159, 10)).toBe('3.1415900000');
  expect(filters.toDecimalOdds(8.2)).toBe('8.20');

任何改善吗?

parseInt比Math.floor快

function floorFigure(figure, decimals){
    if (!decimals) decimals = 2;
    var d = Math.pow(10,decimals);
    return (parseInt(figure*d)/d).toFixed(decimals);
};

floorFigure(123.5999)    =>   "123.59"
floorFigure(123.5999, 3) =>   "123.599"

下面的代码对我来说很好:

num.toString().match(/.\*\\..{0,2}|.\*/)[0];

这里的答案对我没有帮助，它总是四舍五入，或者给我错误的小数。

我的解决方案将您的小数转换为字符串，提取字符，然后将整个东西作为数字返回。

function Dec2(num) {
  num = String(num);
  if(num.indexOf('.') !== -1) {
    var numarr = num.split(".");
    if (numarr.length == 1) {
      return Number(num);
    }
    else {
      return Number(numarr[0]+"."+numarr[1].charAt(0)+numarr[1].charAt(1));
    }
  }
  else {
    return Number(num);
  }  
}

Dec2(99); // 99
Dec2(99.9999999); // 99.99
Dec2(99.35154); // 99.35
Dec2(99.8); // 99.8
Dec2(10265.985475); // 10265.98

num = 19.66752
f = num.toFixed(3).slice(0,-1)
alert(f)

这将返回19.66