JavaScript变量在for循环中变化

Question

i have this for loop:

for (var i = 0; i < pictures.length; i++) {
    var mod = i % 4;
    alert(mod); // first
    //get the current row
    if (mod == 0)
    {
        alert(mod); //second
        tableBody.innerHTML += "<tr>";
    }
    tableBody.innerHTML += "<td><img style='width:146px; height:146px;' src='" + pictures[i].source + "'></td>";
    if (mod == 0)
        tableBody.innerHTML += "</tr>";
}

how come my first alert shows the result of the math calculation inside "mod" variable, and the second alert show always zero ??

Answer 1

因为当且仅当mod == 0时才执行第二个警报。

Answer 2

第二个警报将显示0，因为你有一个if（）语句，它检查mod == 0

Answer 3

C'mon your second alert is inside if() statement. It will get executed only when mod=0. If mod=0, it will enter if loop and execute the statements there. Your if statement contains alert(mod). So, it will print the value of mod which is equal to zero. And in your first alert, it will calculate the value of mod and will print whatever is the value of variable mod(irrsepective of the fact whether it is zero).