SOURCE

//判断输入的值是否为整数
function isInt(num){
    var result=false;
    if(parseInt(num)==parseFloat(num)){
        result=true;
    }
    else{
        result=false;
    }
    return result;
}

if (isInt(15)){
    document.write('15 is a int'+'</br>');
}

document.write("<br>----------------------</br>");

//注：js没有指定的数据类型，所以不区分整数和小数，需要转化
//判断输入的值是否为小数
function isFloat(num){
    var result=false;
    if(parseInt(num)!=parseFloat(num)){
        result=true;
    }
    else{
        result=false;
    }
    return result;
}

if(isFloat(15.15)){
    document.write('15.15 is a float'+'</br>');

}

document.write("<br>----------------------</br>");



//判断输入的值是否为水仙花数
function waterFlower(num1){
    
    if(num1>=100&&num1<=999){
    var gewei=parseInt(num1%10);  
    var shiwei=parseInt((num1/10)%10);
    var baiwei=parseInt(num1/100);
        if((gewei*gewei*gewei+shiwei*shiwei*shiwei+baiwei*baiwei*baiwei)==num1){
            document.write(num1+'is a waterFlower'+'</br>');
        }
        else{
            document.write(num1+'  is not waterflower'+'</br>')
        }          
    }
    else{
            document.write(num1+'  is not range'+'</br>');
        }
}
waterFlower(407);

document.write("<br>----------------------</br>");


//输出所有水仙花树
function waterFlower1(num2){
    var gewei=parseInt(num2%10);  
    var shiwei=parseInt((num2/10)%10);
    var baiwei=parseInt(num2/100);
        if((gewei*gewei*gewei+shiwei*shiwei*shiwei+baiwei*baiwei*baiwei)==num2){
            return true;
        }
        else{
            return false;
        }  
}

for(i=100;i<=999;i++){
    if(waterFlower1(i)){
        document.write(i+'</br>');
    }
}

    <script>
        //单项选择
        var a0=5;
        var b0=6;
        if(a0<b0){
            document.write(a0+'</br>');
        }
        //双向选择
        var a1=1;
        var b1=2;
        var c1;
        if(a1>b1){
            c1=a1;
        }
        else{
            c1=b1;
        }
        document.write(c1+'</br>');

//多项选择(有多个else if 最多只有一个else)
        var a2=8;
        var b2=8;
        if(a2<b2){
            document.write(a2+'</br>');
        } 
        else if(b2>a2){
            document.write(a2+'</br>');
        }
        else{
            document.write(true+'</br>');
        }


        //嵌套循坏
        var a3= 3;
        var b3=4;
        if(a3>b3){
            document.write(a3+'</br>');
        }else{
            if(a3<b3){
                document.write(b3+'</br>');
            }
        }
        
    </script>