我在MDN上找到了这个。他们的方法避免了前面提到的1.005的问题。

函数roundToTwo（num）{return+（数学舍入（num+“e+2”）+“e-2”）；}console.log（“1.005=>”，roundToTwo（1.005））；console.log（'10=>'，roundToTwo（10））；console.log（'1.7777777=>'，roundToTwo（1.7777777））；console.log（'9.1=>'，roundToTwo（9.1））；console.log（'1234.5678=>'，roundToTwo（1234.5678））；

我的解决方案将输入视为字符串，并使用n位数字的“数学舍入”算法：取n位数字，如果数字n+1等于或大于5，则加1。它还允许指定负数，例如，将123.45舍入为-1的数字为120。它也适用于科学符号（例如1.2e-3）。我没有测量它的速度，我认为这不是最好的表现。

function safeRound( numInput, numPrecision ) {
    const strNumber = numInput.toString().replace( 'E', 'e' );
    const bSign = '+-'.indexOf( strNumber[ 0 ] ) !== -1;
    const strSign = bSign  ?  strNumber[ 0 ]  :  '';
    const numSign = strSign !== '-'  ?  +1  :  -1;
    const ixExponent = ( ixFound => ixFound !== -1  ?  ixFound  :  strNumber.length )( strNumber.indexOf( 'e' ) );
    const strExponent = strNumber.substr( ixExponent + 1 );
    const numExponent = ixExponent !== strNumber.length  ?  Number.parseInt( strExponent )  :  0;
    const ixDecimal = ( ixFound => ixFound !== -1  ?  ixFound  :  ixExponent )( strNumber.indexOf( '.' ) );
    const strInteger = strNumber.substring( !bSign  ?  0  :  1, ixDecimal );
    const strFraction = strNumber.substring( ixDecimal + 1, ixExponent );
    
    const numPrecisionAdjusted = numPrecision + numExponent;
    const strIntegerKeep = strInteger.substring( 0, strInteger.length + Math.min( 0, numPrecisionAdjusted ) ) + '0'.repeat( -Math.min( 0, numPrecisionAdjusted ) );
    const strFractionKeep = strFraction.substring( 0, Math.max( 0, numPrecisionAdjusted ) );
    const strRoundedDown = strSign + ( strIntegerKeep === ''  ?  '0'  :  strIntegerKeep ) + ( strFractionKeep === ''  ?  ''  :  '.' + strFractionKeep ) + ( strExponent === ''  ?  ''  :  'e' + strExponent );
    
    const chRoundUp = 0 <= numPrecisionAdjusted  ?  strFraction.substr( numPrecisionAdjusted, 1 )  :  ( '0' + strInteger ).substr( numPrecisionAdjusted, 1 );
    const bRoundUp = '5' <= chRoundUp && chRoundUp <= '9';
    const numRoundUp = bRoundUp  ?  numSign * Math.pow( 10, -numPrecision )  :  0;
    
    return Number.parseFloat( strRoundedDown ) + numRoundUp;
}

function safeRoundTest( numInput, numPrecision, strExpected ) {
    const strActual = safeRound( numInput, numPrecision ).toString();
    const bPassed = strActual === strExpected;
    console.log( 'numInput', numInput, 'numPrecision', numPrecision, 'strExpected', strExpected, 'strActual', strActual, 'bPassed', bPassed );
    return bPassed  ?  0  :  1;
}

function safeRoundTests() {
    let numFailed = 0;
    numFailed += safeRoundTest( 0, 0, '0' );
    numFailed += safeRoundTest( '0', 0, '0' );
    numFailed += safeRoundTest( '0.1', 0, '0' );
    numFailed += safeRoundTest( '+0.1', 0, '0' );
    numFailed += safeRoundTest( '-0.1', 0, '0' );
    numFailed += safeRoundTest( '0.1', 1, '0.1' );
    numFailed += safeRoundTest( '+0.1', 1, '0.1' );
    numFailed += safeRoundTest( '-0.1', 1, '-0.1' );
    numFailed += safeRoundTest( '0.9', 0, '1' );
    numFailed += safeRoundTest( '+0.9', 0, '1' );
    numFailed += safeRoundTest( '-0.9', 0, '-1' );
    numFailed += safeRoundTest( '0.9', 1, '0.9' );
    numFailed += safeRoundTest( '+0.9', 1, '0.9' );
    numFailed += safeRoundTest( '-0.9', 1, '-0.9' );
    numFailed += safeRoundTest( '0.5', 0, '1' );
    numFailed += safeRoundTest( '+0.5', 0, '1' );
    numFailed += safeRoundTest( '-0.5', 0, '-1' );
    numFailed += safeRoundTest( '0.4999', 0, '0' );
    numFailed += safeRoundTest( '+0.4999', 0, '0' );
    numFailed += safeRoundTest( '-0.4999', 0, '0' );
    numFailed += safeRoundTest( '1.005', 2, '1.01' );
    numFailed += safeRoundTest( '1.00499999999', 2, '1' );
    numFailed += safeRoundTest( '012.3456', -4, '0' );
    numFailed += safeRoundTest( '012.3456', -3, '0' );
    numFailed += safeRoundTest( '012.3456', -2, '0' );
    numFailed += safeRoundTest( '012.3456', -1, '10' );
    numFailed += safeRoundTest( '012.3456', 0, '12' );
    numFailed += safeRoundTest( '012.3456', 1, '12.3' );
    numFailed += safeRoundTest( '012.3456', 2, '12.35' );
    numFailed += safeRoundTest( '012.3456', 3, '12.346' );
    numFailed += safeRoundTest( '012.3456', 4, '12.3456' );
    numFailed += safeRoundTest( '012.3456', 5, '12.3456' );
    numFailed += safeRoundTest( '12.', 0, '12' );
    numFailed += safeRoundTest( '.12', 2, '0.12' );
    numFailed += safeRoundTest( '0e0', 0, '0' );
    numFailed += safeRoundTest( '1.2e3', 0, '1200' );
    numFailed += safeRoundTest( '1.2e+3', 0, '1200' );
    numFailed += safeRoundTest( '1.2e-3', 0, '0' );
    numFailed += safeRoundTest( '1.2e-3', 3, '0.001' );
    numFailed += safeRoundTest( '1.2e-3', 4, '0.0012' );
    numFailed += safeRoundTest( '1.2e-3', 5, '0.0012' );
    numFailed += safeRoundTest( '+12.', 0, '12' );
    numFailed += safeRoundTest( '+.12', 2, '0.12' );
    numFailed += safeRoundTest( '+0e0', 0, '0' );
    numFailed += safeRoundTest( '+1.2e3', 0, '1200' );
    numFailed += safeRoundTest( '+1.2e+3', 0, '1200' );
    numFailed += safeRoundTest( '+1.2e-3', 0, '0' );
    numFailed += safeRoundTest( '+1.2e-3', 3, '0.001' );
    numFailed += safeRoundTest( '+1.2e-3', 4, '0.0012' );
    numFailed += safeRoundTest( '+1.2e-3', 5, '0.0012' );
    numFailed += safeRoundTest( '-12.', 0, '-12' );
    numFailed += safeRoundTest( '-.12', 2, '-0.12' );
    numFailed += safeRoundTest( '-0e0', 0, '0' );
    numFailed += safeRoundTest( '-1.2e3', 0, '-1200' );
    numFailed += safeRoundTest( '-1.2e+3', 0, '-1200' );
    numFailed += safeRoundTest( '-1.2e-3', 0, '0' );
    numFailed += safeRoundTest( '-1.2e-3', 3, '-0.001' );
    numFailed += safeRoundTest( '-1.2e-3', 4, '-0.0012' );
    numFailed += safeRoundTest( '-1.2e-3', 5, '-0.0012' );
    numFailed += safeRoundTest( '9876.543e210', 0, '9.876543e+213' );
    numFailed += safeRoundTest( '9876.543e210', -210, '9.877e+213' );
    numFailed += safeRoundTest( '9876.543e210', -209, '9.8765e+213' );
    numFailed += safeRoundTest( '9876.543e+210', 0, '9.876543e+213' );
    numFailed += safeRoundTest( '9876.543e+210', -210, '9.877e+213' );
    numFailed += safeRoundTest( '9876.543e+210', -209, '9.8765e+213' );
    numFailed += safeRoundTest( '9876.543e-210', 213, '9.876543e-207' );
    numFailed += safeRoundTest( '9876.543e-210', 210, '9.877e-207' );
    numFailed += safeRoundTest( '9876.543e-210', 211, '9.8765e-207' );
    console.log( 'numFailed', numFailed );
}

safeRoundTests();

问题是四舍五入到两位小数。

让我们不要把这个复杂化，修改原型链等。

以下是单线解决方案

让round2dec=num=>数学舍入（num*100）/100；控制台日志（round2dec（1.77））；控制台日志（round2dec（1.774））；控制台日志（round2dec（1.777））；console.log（round2dec（10））；

舍入问题可以通过使用指数表示法来避免。

public roundFinancial(amount: number, decimals: number) {
    return Number(Math.round(Number(`${amount}e${decimals}`)) + `e-${decimals}`);
}

这是astorije的答案的修改版本，更好地支持负值舍入。

// https://stackoverflow.com/a/21323513/384884
// Modified answer from astorije
function round(value, precision) {
    // Ensure precision exists
    if (typeof precision === "undefined" || +precision === 0) {
        // Just do a regular Math.round
        return Math.round(value);
    }

    // Convert the value and precision variables both to numbers
    value = +value;
    precision = +precision;

    // Ensure the value is a number and that precision is usable
    if (isNaN(value) || !(typeof precision === "number" && precision % 1 === 0)) {
        // Return NaN
        return NaN;
    }

    // Get the sign of value
    var signValue = Math.sign(value);

    // Get the absolute value of value
    value = Math.abs(value);

    // Shift
    value = value.toString().split("e");
    value = Math.round(+(value[0] + "e" + (value[1] ? (+value[1] + precision) : precision)));

    // Shift back
    value = value.toString().split("e");
    value = +(value[0] + "e" + (value[1] ? (+value[1] - precision) : -precision));

    // Apply the sign
    value = value * signValue;

    // Return rounded value
    return value;
}

我尝试了自己的代码。试试看：

function AmountDispalyFormat(value) {
    value = value.toFixed(3);
    var amount = value.toString().split('.');
    var result = 0;
    if (amount.length > 1) {
        var secondValue = parseInt(amount[1].toString().slice(0, 2));
        if (amount[1].toString().length > 2) {
            if (parseInt(amount[1].toString().slice(2, 3)) > 4) {
                secondValue++;
                if (secondValue == 100) {
                    amount[0] = parseInt(amount[0]) + 1;
                    secondValue = 0;
                }
            }
        }

        if (secondValue.toString().length == 1) {
            secondValue = "0" + secondValue;
        }
        result = parseFloat(amount[0] + "." + secondValue);
    } else {
        result = parseFloat(amount);
    }
    return result;
}