留神项

  • 所有含浮点数的裸加减乘除都有可能触发精度问题；如0.1+0.2；4100.065 * 100

具体实现

1. 乘法：

function mul(a,b){    let c = 0,          d = a.toString(),          e = b.toString();    try {        c += d.split(".")[1].length;    } catch (f) {}    try {        c += e.split(".")[1].length;    } catch (f) {}    return Number(d.replace(".", "")) * Number(e.replace(".", "")) / Math.pow(10, c);  }

2. 加法

function add(a,b){    let c, d, e;    try {        c = a.toString().split(".")[1].length;    } catch (f) {        c = 0;    }    try {        d = b.toString().split(".")[1].length;    } catch (f) {        d = 0;    }    e = Math.pow(10, Math.max(c, d));    return  (mul(a, e) + mul(b, e)) / e;}

3. 减法

function sub(a, b) {    let c, d, e;    try {        c = a.toString().split(".")[1].length;    } catch (f) {        c = 0;    }    try {        d = b.toString().split(".")[1].length;    } catch (f) {        d = 0;    }    e = Math.pow(10, Math.max(c, d));    return (mul(a, e) - mul(b, e)) / e;}

4. 除法

function divide(a, b) {    var c, d, e = 0,           f = 0;    try {        e = a.toString().split(".")[1].length;    } catch (g) {        e = 0;    }    try {        f = b.toString().split(".")[1].length;    } catch (g) {        f = 0;    }    c = Number(a.toString().replace(".", ""));    d = Number(b.toString().replace(".", ""));    return mul(c / d, Math.pow(10, f - e));}

5. 浮点数四舍五入,保留固定小数位(不加入运算，纯展现)

function round(num, precision) {  const base = Math.pow(10, precision)  return (Math.round((num.toPrecision(17) * base).toFixed(1)) / base).toFixed(precision)}

todo 升级版

  1. 思考写成科里化模式 待做
  2. 思考大数状况 待做