Javascript 检查数字是否=变量

Question

var Period =1;

        if(Period==1){
            document.getElementById("Main").style.backgroundImage = "url('Main_Background_Grass_1.png')";
        }

由于某种原因，这不起作用。图像位置是正确的，但我确定有问题。

我对 javascript 还很陌生

这里有更多代码

<script type="text/javascript">

        var Knowledge = 0;
        var Period =1;

        if(Period==1){
            document.getElementById("Main").style.backgroundImage = "url('Main_Background_Grass_1.png')";
        }

</script>

<div id="Main">

    <div id="Toolbar">
        Oh noes! Something Went Wrong
    </div>
</div>

图像根本不会显示

Answer 1

调用函数时未找到该元素，请将 JavaScript 放在结束正文标记之前

<div id="Main">

    <div id="Toolbar">
        Oh noes! Something Went Wrong
    </div>
</div>

<script type="text/javascript">

        var Knowledge = 0;
        var Period =1;

        if(Period==1){
            document.getElementById("Main").style.backgroundImage = "url('Main_Background_Grass_1.png')";
        }

</script>