我的JavaScript有什么问题？

Question

I have this bit of javascript and php:

function change(){

var heading = "<?= $heading ?>";
var description = "<?= $description ?>";
var valid = "<?= $valid ?>";
var background = "<?= $background ?>";
alert("hi");
    switch(background){
        case 1:
        document.getElementById('main').style.backgroundImage = "(url"img/bg1.jpg")";
        break;

        case 2:

        break;

        case 3:

        break;

        default:
        break;
    }
}

If I remove the case 1, the line: document.getElementById('main').style.backgroundImage = "(url"img/bg1.jpg")"; the function will work, I'll get the hi alert. But if its in there it doesn't work at all. But I've used that line of code before and its worked, why does it cause this script to stop working?

TIA

Answer 1

尝试将该行替换为：

document.getElementById('main').style.backgroundImage = "url('img/bg1.jpg')";

Answer 2

case 1 should be as below

case 1:
    document.getElementById('main').style.backgroundImage = "url("img/bg1.jpg")";
    break;