計算數字時Javascript返回意外值

Question

請參閱代碼段，計算數字時javascript會返回意外值。我正在使用最新的Firefox。有沒有一種方法可以始終獲得正確的價值？

console.log(100+59.59, "expected 159.59"); 
 
console.log(200+59.59, "expected 259.59"); 
 
console.log(300+59.59, "expected 359.59"); 
 
console.log(400+59.59, "expected 459.59"); 
 
console.log(500+59.59, "expected 559.59"); 
 
console.log(600+286.59, "expected 886.59"); 
 
console.log(700+286.59, "expected 986.59");

Answer 1

function FloatAdd(arg1, arg2) 
{ 
    var r1, r2, m; 
    try { r1 = arg1.toString().split(".")[1].length; } catch (e) { r1 = 0; } 
    try { r2 = arg2.toString().split(".")[1].length; } catch (e) { r2 = 0; } 
    m = Math.pow(10, Math.max(r1, r2)); 
    return (FloatMul(arg1, m) + FloatMul(arg2, m))/m; 
} 

function FloatSubtraction(arg1, arg2) 
{ 
    var r1, r2, m, n; 
    try { r1 = arg1.toString().split(".")[1].length } catch (e) { r1 = 0 } 
    try { r2 = arg2.toString().split(".")[1].length } catch (e) { r2 = 0 } 
    m = Math.pow(10, Math.max(r1, r2)); 
    n = (r1 >= r2) ? r1 : r2; 
    return ((arg1 * m - arg2 * m)/m).toFixed(n); 
} 

function FloatMul(arg1, arg2) 
{ 
    var m = 0, s1 = arg1.toString(), s2 = arg2.toString(); 
    try { m += s1.split(".")[1].length; } catch (e) { } 
    try { m += s2.split(".")[1].length; } catch (e) { } 
    return Number(s1.replace(".", "")) * Number(s2.replace(".", ""))/Math.pow(10, m); 
} 

function FloatDiv(arg1, arg2) 
{ 
    var t1 = 0, t2 = 0, r1, r2; 
    try { t1 = arg1.toString().split(".")[1].length } catch (e) { } 
    try { t2 = arg2.toString().split(".")[1].length } catch (e) { } 
    with (Math) 
    { 
    r1 = Number(arg1.toString().replace(".", "")) 
    r2 = Number(arg2.toString().replace(".", "")) 
    return (r1/r2) * pow(10, t2 - t1); 
    } 
} 

參考http://kevintsengtw.blogspot.tw/2011/09/javascript.html

這個問題已經在這裏有一個答案：
Is floating point math broken?

所以快速的方法是轉換爲字符串，然後改爲浮動再次修復它

Answer 2

如果您確定您不需要超過x小數位，您可以使用toFixed()方法，如下所示：

console.log((100+59.59).toFixed(2), "expected 159.59"); 
 
console.log((200+59.59).toFixed(2), "expected 259.59"); 
 
console.log((300+59.59).toFixed(2), "expected 359.59"); 
 
console.log((400+59.59).toFixed(2), "expected 459.59"); 
 
console.log((500+59.59).toFixed(2), "expected 559.59"); 
 
console.log((600+286.59).toFixed(2), "expected 886.59"); 
 
console.log((700+286.59).toFixed(2), "expected 986.59");

這裏的問題不是使用Javascript，但浮點數以二進制的侷限性。 0.59不能用64位浮點數完美表示（實際上，當轉換回十進制時，它實際上運行到0.58999999999999996891375531049561686813831329345703125）。