JS浮点数运算——精度丢失解决方案

//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)
}

//加法

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.mul(m) + Number(arg).mul(m) ).div(m); 
}

//减法

Number.prototype.sub = function(arg) {
    return this.add(-arg);
}
//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) {}
    r1 = Number(this.toString().replace(".", ""))
    r2 = Number(arg.toString().replace(".", ""))
    return(r1 / r2) *  Math.pow(10, t2 - t1);
}

//四舍五入保留两位 n 数
Number.prototype.toFixed = function(n){
    var times = Math.pow(10, n)
    var des = this * times + 0.5
    des = parseInt(des, 10) / times
    return des + '';

}