JS 丢失精度的问题在网上一搜一大片，所以我就找了一个使用
Number.prototype.mul = function (a) { var b = 0, c = this.toString(), d = a.toString(); try { b += c.split(".")[1].length } catch (e) {} try { b += d.split(".")[1].length } catch (e) {} return Number(c.replace(".", "")) * Number(d.replace(".", "")) / Math.pow(10, b) }, Number.prototype.divide = function (a) { var d, e, b = 0, c = 0; try { b = this.toString().split(".")[1].length } catch (f) {} try { c = a.toString().split(".")[1].length } catch (f) {} return d = Number(this.toString().replace(".", "")), e = Number(a.toString().replace(".", "")), d / e * Math.pow(10, c - b) }, Number.prototype.add = function (a) { var b, c, d; try { b = a.toString().split(".")[1].length } catch (e) { b = 0 } try { c = this.toString().split(".")[1].length } catch (e) { c = 0 } return d = Math.pow(10, Math.max(b, c)), (a * d + this * d) / d }, Number.prototype.subtract = function (a) { var b, c, d, e; try { b = this.toString().split(".")[1].length } catch (f) { b = 0 } try { c = a.toString().split(".")[1].length } catch (f) { c = 0 } return d = Math.pow(10, Math.max(b, c)), e = b >= c ? b : c, Number(((this * d - a * d) / d).toFixed(e)) };
在这个代码中 add和subtract方法 在返回操作时仍然使用的浮点计算的，所以依然会出现精度丢失的情况。
add方法
return d = Math.pow(10, Math.max(b, c)), (a * d + this * d) / d
这个记的地方应该是改为 return d = Math.pow(10, Math.max(b, c)), (a.mul(d) + this.mul(d)) / d
同样subtract这个地方也存在同样的问题。
修改后的全部代码为
Number.prototype.mul = function (a) { var b = 0, c = this.toString(), d = a.toString(); try { b += c.split(".")[1].length } catch (e) {} try { b += d.split(".")[1].length } catch (e) {} return Number(c.replace(".", "")) * Number(d.replace(".", "")) / Math.pow(10, b) }, Number.prototype.divide = function (a) { var d, e, b = 0, c = 0; try { b = this.toString().split(".")[1].length } catch (f) {} try { c = a.toString().split(".")[1].length } catch (f) {} return d = Number(this.toString().replace(".", "")), e = Number(a.toString().replace(".", "")), d / e * Math.pow(10, c - b) }, Number.prototype.add = function (a) { var b, c, d; try { b = a.toString().split(".")[1].length } catch (e) { b = 0 } try { c = this.toString().split(".")[1].length } catch (e) { c = 0 } return d = Math.pow(10, Math.max(b, c)), (a.mul(d) + this.mul(d)) / d }, Number.prototype.subtract = function (a) { var b, c, d, e; try { b = this.toString().split(".")[1].length } catch (f) { b = 0 } try { c = a.toString().split(".")[1].length } catch (f) { c = 0 } return d = Math.pow(10, Math.max(b, c)), e = b >= c ? b : c, Number(((this.mul(d) - a.mul(d)) / d).toFixed(e)) };