1       add(a, b) {//相加
 2           var c, d, e;
 3           try {
 4             c = a.toString().split(".")[1].length;
 5           } catch (f) {
 6             c = 0;
 7           }
 8           try {
 9             d = b.toString().split(".")[1].length;
10           } catch (f) {
11             d = 0;
 
12           }
13           return e = Math.pow(10, Math.max(c, d)), (this.mul(a, e) + this.mul(b, e)) / e;
14       },
15       sub(a, b) {//相減
16         var c, d, e;
17         try {
18           c = a.toString().split(".")[1].length;
19         } catch (f) {
20           c = 0;
21         }
22         try
 
 {
23           d = b.toString().split(".")[1].length;
24         } catch (f) {
25           d = 0;
26         }
27         return e = Math.pow(10, Math.max(c, d)), (this.mul(a, e) - this.mul(b, e)) / e;
28       },
29       mul(a, b) {//主體
30         var c = 0,
31           d = a.toString(),
32           e = b.toString();
 
33         try {
34           c += d.split(".")[1].length;
35         } catch (f) { }
36         try {
37           c += e.split(".")[1].length;
38         } catch (f) { }
39         return Number(d.replace(".", "")) * Number(e.replace(".", "")) / Math.pow(10, c);
40       },
41       div(a, b) {//除
42         var c, d, e = 0,
43           f = 0;
44         try {
45           e = a.toString().split(".")[1].length;
46         } catch (g) { }
47         try {
48           f = b.toString().split(".")[1].length;
49         } catch (g) { }
50         return c = Number(a.toString().replace(".", "")), d = Number(b.toString().replace(".", "")), this.mul(c / d, Math.pow(10, f - e));
51       }

js在數字計算時，因為IEEE 754會有精度丟失，完善一下，需要用到哪個，只要mul和你用到的函數就OK

JS數字計算精度問題解決