常见例子  

// 加法
0.1 + 0.2 = 0.30000000000000004
0.1 + 0.7 = 0.7999999999999999
0.2 + 0.4 = 0.6000000000000001
 
// 减法
0.3 - 0.2 = 0.09999999999999998
1.5 - 1.2 = 0.30000000000000004
 
// 乘法
0.8 * 3 = 2.4000000000000004
19.9 * 100 = 1989.9999999999998
 
// 除法
0.3 / 0.1 = 2.9999999999999996
0.69 / 10 = 0.06899999999999999
 
// 比较
0.1 + 0.2 === 0.3 // false
(0.3 - 0.2) === (0.2 - 0.1) // false

解决方法

1. 加

   Vue.prototype.NumberAdd = function(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);
   }

2. 减

   Vue.prototype.NumberSub = function(arg1, arg2) {
       var re1, re2, m, n;
       try {
           re1 = arg1.toString().split(".")[1].length;
       } catch (e) {
       re1 = 0;
       }
       try {
           re2 = arg2.toString().split(".")[1].length;
       } catch (e) {
           re2 = 0;
       }
       m = Math.pow(10, Math.max(re1, re2)); 
       n = (re1 >= re2) ? re1 : re2;
       return ((arg1 * m - arg2 * m) / m).toFixed(n);
   }

3. 乘

   Vue.prototype.NumberMul = function(arg1, arg2) {
       var m = 0;
       var s1 = arg1.toString();
       var 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);
   }

4. 除

   // 除数，被除数， 保留的小数点后的位数
   Vue.prototype.NumberDiv = function (arg1,arg2,digit){
       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){}
       r1=Number(arg1.toString().replace(".",""))
       r2=Number(arg2.toString().replace(".",""))
       //获取小数点后的计算值
      var result= ((r1/r2)*Math.pow(10,t2-t1)).toString()
       var result2=result.split(".")[1];
       result2=result2.substring(0,digit>result2.length?result2.length:digit);
    
       return Number(result.split(".")[0]+"."+result2);
   }

   原文地址