解决精度问题js精确计算

解决精度问题js精确计算

//加  Number.prototype.add = function(arg) {      var r1, r2, m;      try{r1 = this.toString().split(".")[1].length;}catch(e){r1 = 0;}      try{r2 = arg.toString().split(".")[1].length;}catch(e){r2 = 0;}      m = Math.pow(10, Math.max(r1, r2));      return (this * m + arg * m) / m;  };  // 减法  Number.prototype.sub = function(arg) {      return this.add(-arg);  };     // 乘法  Number.prototype.mul = function(arg) {      var m = 0, s1 = this.toString(), s2 = arg.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);  };  // 除法  Number.prototype.div = function(arg) {      var t1 = 0, t2 = 0, r1, r2;      try {t1 = this.toString().split(".")[1].length;}catch(e){}      try {t2 = arg.toString().split(".")[1].length;}catch(e){}      with (Math) {          r1 = Number(this.toString().replace(".", ""));          r2 = Number(arg.toString().replace(".", ""));          return (r1 / r2) * pow(10, t2 - t1);      }  };        //test  var a = 0.4;  var b = 0.3;  alert(Number(a).sub(b));