SOURCE

/* function multiply(a, b) {
    let countA = ''.split.call(a,'.')[1]?''.split.call(a,'.')[1].length:0
    let countB = ''.split.call(b,'.')[1]?''.split.call(b,'.')[1].length:0
    console.log(countA,countB)
    return (a*b).toFixed(countA+countB)
} */



function multiply(a, b) {
    //var reg = /(\d+\.)|(\d+)/;
    var reg = /\d*[\.\d]/;
    var la = a.toString().replace(reg,"").length,
        lb = b.toString().replace(reg,"").length; 


    console.log()
    return (a*b).toFixed(la+lb);
}
console.log(multiply(3, 0.1))