JS的精确简单的加减乘除

<script>

function decNum(a){/*获取小数位数*/

    var r=0;

    a=a.toString();

    if(a.indexOf(".")!== -1) r=a.split(".")[1].length;

    return r;

}

function int(a){/*去除小数点并转成数值*/

    return parseInt(a.toString().replace(".",""));

}

function calc(a,b,type){//加减乘除

    var r,

        da=decNum(a),

        db=decNum(b),

        dsum=da+db,

        dmin=Math.min(da,db),

        dmax=Math.max(da,db);

    dsum+=dmax-dmin;

    dsum=Math.pow(10,dsum);

    dmax=Math.pow(10,dmax);

    a=int(a);

    b=int(b);

    if(da>db){

        b*=Math.pow(10,da-db);

    }else{

        a*=Math.pow(10,db-da);

    }

    switch(type){

        case "add":

            r=(a+b)/dmax;

            break;

        case "subtract":

            r=(a-b)/dmax;

            break;

        case "multiply":

            r=(a*b)/dsum;

            break;

        case "divide":

            r=a/b;

            break;

    }

    return r;

}

s=calc(0.1,0.2,"add");

console.log(s);

s=calc(-0.1,0.2,"add");

console.log(s);

s=calc(0.2,0.1,"subtract");

console.log(s);

s=calc(0.002,0.01,"multiply");

console.log(s);

s=calc(2.2,100,"divide");

console.log(s);

</script>