为什么我的Javascript代码无法正常工作？

Question

I recently started working with Javascript, like a few hours ago, and I can't figure out why it's still showing text it shouldn't be on my website. Dreamweaver says no error, but there has to be..

<script type="text/javascript">
     var day = new Date();
     var hr = day.getHours();
     if((hr == 1) || (hr == 2) || (hr == 3) || (hr == 4) || (hr == 5) || (hr == 6) || (hr == 7) || (hr == 8) || (hr == 9)); {
         document.write("Paragraph one stack example");
     }
    if(hr == 10) {
        document.write("P2 stack ex");
    }
    if((hr == 11) || (hr == 12) || (hr == 13)); {
        document.write("P3 stack ex.");
    }

</script>

Answer 1

From your code, slightly reformatted:

if((hr == 1) || ... || (hr == 9)); {
    document.write("Paragraph one stack example");
}

Get rid of that semicolon, it's making the entire if bit irrelevant.

What it translates to is:

if((hr == 1) || ... || (hr == 9))
    ;
{
    document.write("Paragraph one stack example");
}

In other words,

• if hr is 1-9, do nothing.
• regardless of the value of hr , output "Paragraph one stack example".

You have the same problem with the if statement for 11/12/13 as well.

---

A better solution for that "one through nine" if statement, by the way, would be:

if((hr >= 1) && (hr <= 9)) {
    document.write("Paragraph one stack example");
}

and you can further clean up the code since all the conditions are mutually exclusive:

<script type="text/javascript">
    var day = new Date();
    var hr = day.getHours();
    if ((hr >= 1) || (hr <= 9)) {
        document.write("Paragraph one stack example");
    } else if (hr == 10) {
        document.write("P2 stack ex");
    } else if ((hr >= 11) && (hr <= 13)) {
        document.write("P3 stack ex.");
    }
</script>

There's little point checking if hr is equal to 10 if you've already established that it's 4 , for example. So you can use else if for that.

Answer 2

Code is valid, but you have done mistake when put

;

at the end of if expression

if you remove this all will works fine!

 var day = new Date(); var hr = day.getHours(); if((hr == 1) || (hr == 2) || (hr == 3) || (hr == 4) || (hr == 5) || (hr == 6) || (hr == 7) || (hr == 8) || (hr == 9)) { document.write("Paragraph one stack example"); } if(hr == 10) { document.write("P2 stack ex"); } if((hr == 11) || (hr == 12) || (hr == 13)) { document.write("P3 stack ex."); }