我固定使用以下简单的方法-

var num = 15.7784514;
Math.floor(num*100)/100;

结果是15.77

下面的代码对我来说很好:

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

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?

我也面临着同样的问题，并决定在TS中使用字符串操作。

如果没有足够的小数，它将返回原始值

const getDecimalsWithoutRounding = (value: number, numberOfDecimals: number) => {
  const stringValue: string = value?.toString();
  const dotIdx: number = stringValue?.indexOf('.');
  if (dotIdx) {
    return parseFloat(stringValue.slice(0, dotIdx + numberOfDecimals + 1));
  } else {
    return value;
  }
};

console.log(getDecimalsWithoutRounding(3.34589, 2)); /// 3.34
console.log(getDecimalsWithoutRounding(null, 2));  ///null
console.log(getDecimalsWithoutRounding(55.123456789, 5)); /// 55.12345
console.log(getDecimalsWithoutRounding(10, 2));  /// 10
console.log(getDecimalsWithoutRounding(10.6, 5)); /// 10.6

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

这将返回19.66

截断不带零

function toTrunc(value,n){  
    return Math.floor(value*Math.pow(10,n))/(Math.pow(10,n));
}

or

function toTrunc(value,n){
    x=(value.toString()+".0").split(".");
    return parseFloat(x[0]+"."+x[1].substr(0,n));
}

测试:

toTrunc(17.4532,2)  //17.45
toTrunc(177.4532,1) //177.4
toTrunc(1.4532,1)   //1.4
toTrunc(.4,2)       //0.4

用零截断

function toTruncFixed(value,n){
    return toTrunc(value,n).toFixed(n);
}

测试:

toTrunc(17.4532,2)  //17.45
toTrunc(177.4532,1) //177.4
toTrunc(1.4532,1)   //1.4
toTrunc(.4,2)       //0.40