var preMath = function () {    return {        //修复四则运算浮点数精度问题        fixArithmetic: function (m, n, op) {            var a = (m + "");            var b = (n + "");            var x = 1;            var y = 1;            var c = 1;            if (a.indexOf(".") > 0) {                x = Math.pow(10, a.length - a.indexOf(".") - 1);            }            if (b.indexOf(".") > 0) {                y = Math.pow(10, b.length - b.indexOf(".") - 1);            }            switch (op) {                case '+':                    c = Math.max(x, y);                    m = Math.round(m * c);                    n = Math.round(n * c);                    return eval("(" + m + op + n + ")/" + c);                case '-':                    c = Math.max(x, y);                    m = Math.round(m * c);                    n = Math.round(n * c);                    n = -n;                    op = "+";                    return eval("(" + m + op + n + ")/" + c);                case '*':                    c = x * y;                    m = Math.round(m * x);                    n = Math.round(n * y);                    return eval("(" + m + op + n + ")/" + c);                case '/':                    c = Math.max(x, y);                    m = Math.round(m * c);                    n = Math.round(n * c);                    c = 1;                    return eval("(" + m + op + n + ")/" + c);            }        }    };}();