Question

我新到JavaScript，现在我遇到了这个问题：当我启动网页时，“btn”是不可见的（隐藏的），但我需要它才能看到mousedown。这是脚本：

var start= false;
var racket = document.getElementById("racket");
var btn = document.getElementById("btn");
btn.style.visibility = "visible";
btn.onmousedown = Start();

function Start() {
    btn.style.visibility = "hidden";
    start = true;
    document.onclick = RacketClick();
}

function RacketClick() {

}

当我启动网页时，btn被隐藏了......你能帮助我吗？

UPD 1 HTML代码和CSS代码：

<!DOCTYPE html>
<html>
    <head>
        <meta http-equiv="Content-Type" content="text/html; charset=utf-8"/>
        <meta charset="utf-8" />
        <title>Main</title>
        <link href="/css/default.css" rel="stylesheet" />
        <script src="/js/mymain.js"></script>
    </head>
    <body>
        <div id="racket"></div>
        <div id="btn"></div>
    </body>
</html>

#racket {
    top: 100%;
    margin-top: -200px;
    left: 50%;
    margin-left: -77px;
    position: absolute;
    background-image: url('/images/racket.png');
    width: 154px;
    height: 250px;
    animation-name: racketanimation;
    animation-iteration-count: infinite;
    animation-delay: 0s;
    animation-fill-mode: forwards;
    animation-duration: 4s;
    animation-timing-function: linear;
    animation-direction:alternate;
}

@keyframes racketanimation {
    from {
        transform: rotateX(40deg);
    }
    to {
        transform: rotateX(55deg);
    }
}

#btn {
    top: 50%;
    left: 50%;
    position: absolute;
    margin-top: -128px;
    margin-left: -128px; 
    height: 256px; 
    width: 256px;
    background-image: url('/images/playnowborder.png');
    animation-iteration-count: infinite;
    animation-delay: 0s;
    animation-fill-mode: forwards;
    animation-duration: 10s;
    animation-name: clicken;
    animation-timing-function: linear;
}

@keyframes clicken {
    from {
        transform: rotate(360deg);
    }
    to {
        transform: rotate(0deg);
    }
}

我也是这个网站的新手！我希望你的答案，但我没有投票的声誉......

Answer 1

您应该使用不带括号的函数赋值：

btn.onmousedown = Start;

否则函数Start在分配时执行，您的按钮会立即隐藏。

Answer 2

这一行是你的问题：

btn.onmousedown = Start();

您正在执行函数start并将结果（undefined）分配给btn.onmousedown。你应该：

btn.onmousedown = Start;

没有括号，要分配函数，不要调用函数。

JavaScript和可见性

2 个答案: