SOURCE

let a = "1.23";

const checkNotInt=(a)=>{
    if(a){
        let str = String(a);

        let dot_index = str.indexOf(".");
        let not_int_num = str.length - (dot_index+1);
        if(dot_index>-1 && not_int_num>0){
            
            console.log(`是${not_int_num}位小数`)
        }else{
            console.log("不是小数")
        }
        

    }
}

checkNotInt(a);
checkNotInt(123);