JavaScript浮点运算，小数点精度

math.js

// JavaScript Document
//数学函数
// 浮点数加法运算
function floatAdd(arg1, arg2) {
    var r1, r2, m;
    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));
    return (arg1 * m + arg2 * m) / m;
}

// 浮点数减法运算
function floatSub(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);
}

// 浮点数乘法运算
function floatMul(arg1, arg2) {
    var m = 0, s1 = arg1.toString(), 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);
}

// 浮点数除法运算
function floatDiv(arg1, arg2) {
    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) {}
    with(Math) {
        r1 = Number(arg1.toString().replace(".", ""));
        r2 = Number(arg2.toString().replace(".", ""));
        return (r1 / r2) * pow(10, t2 - t1);
    }
}
// 设置数值精度
function setScale(value, scale, roundingMode) {
    if (roundingMode.toLowerCase() == "roundhalfup") {
        return (Math.round(value * Math.pow(10, scale)) / Math.pow(10, scale)).toFixed(scale);
    } else if (roundingMode.toLowerCase() == "roundup") {
        return (Math.ceil(value * Math.pow(10, scale)) / Math.pow(10, scale)).toFixed(scale);
    } else {
        return (Math.floor(value * Math.pow(10, scale)) / Math.pow(10, scale)).toFixed(scale);
    }
}   

原文地址：https://www.cnblogs.com/thatme/p/10208273.html