3 回答

TA貢獻1868條經驗 獲得超4個贊
javascript 中的方法alert
沒有返回值,而 javascript 中的返回值是undefined
.
您將span
內部 html 設置為該值
document.getElementById("no").innerHTML = alert("Sorry, but we're all sold out! Try again later.");
我很好奇你認為上面這行做了什么。

TA貢獻1816條經驗 獲得超6個贊
為什么要設置要提醒的元素的innerHTML?
function purchase() {
alert("Sorry, but we're all sold out! Try again later.");
}
<!--Copyright 2020 AWOL Industries International. All rights reserved-->
<!DOCTYPE html>
<html>
<head profile="http://www.w3.org/2005/10/profile">
<title>Buy stuff at a high price!</title>
<link rel="icon" type="image/png" href="https://cdn.hipwallpaper.com/i/63/61/AykYVG.png">
</head>
<body>
<center>
<h1 style="color:red; background-color:black">AWOL INDUSTRIES INTERNATIONAL</h1>
</center>
<style>
center.mission {
font-family: serrif;
font-size: 180%;
background-color: rgb(100, 200, 0);
LINE-HEIGHT: 1;
}
body {
background-color: rgb(196, 255, 196);
}
</style>
<!--Our products-->
<p>
</br>
<center class="products">
<h1>OUR PRODUCTS</h1>
</center>
<center>
<h3>NO RETURNS</h3>
</center>
<br/>
<div id="column1">Single sheet 8.5"/11" printer paper
<br/>
<img src="https://www.backgroundsy.com/file/large/blank-paper-background.jpg" height="150px" width="350px" />
<button onclick="purchase()">BUY NOW FOR $19.99</button>
</div>
<div id="column2">Single sheet 8.5"/11" printer paper(pre-crumpled)
<br/>
<center><img src="https://149351503.v2.pressablecdn.com/wp-content/uploads/2015/09/paper_71_closed.png" height="150px" width="200px" /></center>
<button onclick="purchase()">BUY NOW FOR $34.99</button>
</div>
<div id="column3">Single CD-R disc, scratched
<br/>
<img src="https://i.redd.it/akbvkcw2xgmz.jpg" height="150px" width="250px" />
<br/>
<button onclick="purchase()">BUY NOW FOR $42.99</button>
</div>
<style>
center.products {
color: green;
background-color: purple;
}
div {
float: left;
height: 200px;
width: 200px;
padding: 0 10px;
}
#column1 {
background-color: lightgrey;
width: 30%;
}
#column2 {
background-color: grey;
width: 30%;
}
#column3 {
background-color: darkgrey;
width: 30%;
}
</style>
<div id="column4">Single toilet paper square for quarentine days
<br/>
<img src="https://photos1.blogger.com/blogger/7265/3234/1600/napkin.jpg" height="150px" width="250px" />
<button onclick="purchase()">BUY NOW FOR $12.99</button>
</div>
<div id="column5">Single use toothpick
<br/>
<center><img src="https://sc02.alicdn.com/kf/HTB1sYpPQpXXXXcPXXXXq6xXFXXXu.jpg" height="150px" width="300px" /></center>
<button onclick="purchase()">BUY NOW FOR $6.99</button>
</div>
<div id="column6">10cm dental floss
<br/>
<img src="https://upload.wikimedia.org/wikipedia/commons/5/53/Dental_floss_%28whole%29.jpg" height="150px" width="250px" />
<br/>
<button onclick="purchase()">BUY NOW FOR $339.99</button>
</div>
<style>
center.products {
color: green;
background-color: purple;
}
div {
float: left;
height: 200px;
width: 200px;
padding: 0 10px;
}
#column4 {
background-color: darkgrey;
width: 30%;
}
#column5 {
background-color: lightgrey;
width: 30%;
}
#column6 {
background-color: grey;
width: 30%;
}
</style>
<!--For click events-->
<span id="no"></span>
</body>
</html>
這將解決您的問題。

TA貢獻1789條經驗 獲得超10個贊
在 javascript 中,任何未定義的變量(或屬性)都是undefined(這是一種類型,如String、Object、Date、null等)。當這個結果被強制轉換為字符串時,它顯示為實際的字符串“未定義”。在瀏覽器的控制臺中嘗試以下操作來感受一下:
console.log(foo);
console.log(window.foo);
console.log(String(window.foo));
當您將 div 的屬性分配給警報函數innerHTML
的結果(它不返回任何內容,因此值為)時,您將其強制轉換為字符串“undefined”并將其設置為分區?您的實際預期行為是什么?undefined
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