解決精度問題js精確計算

解決精度問題js精確計算

//加
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  m + arg  m) / m;
};
// 減法
Number.prototype.sub = function(arg) {
    return this.add(-arg);
};

// 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);
};
// 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){}
    with (Math) {
        r1 = Number(this.toString().replace(".", ""));
        r2 = Number(arg.toString().replace(".", ""));
        return (r1 / r2)  pow(10, t2 - t1);
    }
};
//test
var a = 0.4;
var b = 0.3;
alert(Number(a).sub(b));</pre>