JavaScript在onClick函数中检查字符串是否为空
[英]JavaScript check if string is empty during onClick function
问题描述
Can anyone advise me what is wrong with the empty String check in the JavaScript below. 
谁能告诉我下面的JavaScript中的空String检查有什么问题。
It works fine if I remove the line of code which checks for empty String, but I would like to display "Nothing selected" if the selection is empty. 如果我删除检查空字符串的代码行，它会很好地工作，但是如果选择为空，我想显示“ Nothing selected”。
<html>
<script language="JavaScript">
<!--
function update()
{
var selection = "";
var empty = "";
if (document.form1.TeaName.checked) selection += "Tea<br>";
if (document.form1.CoffeeName.checked) selection += "Coffee<br>";
if (document.form1.EggsName.checked) selection += "Eggs<br>";
if (document.form1.BaconName.checked) selection += "Bacon<br>";
if (selection.equals(empty)) selection = "Nothing selected.";
document.getElementById("currentSelection").innerHTML = selection;
}
-->
</script>
<body>
<form name="form1">
<div id="container" style="width:100%">
<div id="left" style="float:left; width: 30%;">
<h3>List 1</h3>
<input type="checkbox" onClick="update()" name="TeaName" value="Tea">Tea<br>
<input type="checkbox" onClick="update()" name="CoffeeName" value="Coffee">Coffee<br>
</div>
<div id="middle" style="float:left; width: 30%;">
<h3>List 2</h3>
<input type="checkbox" onClick="update()" name="EggsName" value="Eggs">Eggs<br>
<input type="checkbox" onClick="update()" name="BaconName" value="Bacon">Bacon<br>
</div>
<div id="right" style="float:left; width: 30%;">
<h3>Currently selected</h3>
<p id="currentSelection">Please make a selection.</p>
</div>
</div>
</form>
</body>
</html>
Thank you for your time, 感谢您的时间，
James 詹姆士
5 个解决方案
解决方案1
3 已采纳 2015-11-05 23:44:25
There's no such method equals . 没有这样的方法equals 。 Don't complicate things: 不要使事情复杂化：
if (selection.length === 0) selection = "Nothing selected.";
解决方案2
2 2015-11-05 23:48:04
replace this row: 替换此行：
if (selection.equals(empty)) selection = "Nothing selected.";
with this: 有了这个：
if (selection == "" ) selection = "Nothing selected.";
解决方案3
0 2015-11-05 23:51:41
尝试这个
if(!selection) selection="Nothing selected.";
解决方案4
0 2015-11-05 23:54:47
There is no equals function in javascript, you either have to check with the length or a simple === operator javascript中没有equals函数，您必须检查长度或简单的===运算符
if (selection.length<= 0) selection = "Nothing selected.";
(OR)
if(selection === "") selection = "Nothing selected";
(OR)
selection=(selection.length > 0) ? selection : "Nothing selected";
The function equals you have used should be related to some javascript library or framework. 您使用过的函数应该与某些javascript库或框架相关。
解决方案5
0
You can simply have default text and skip the last check. 您可以简单地使用默认文本并跳过最后的检查。
var selection = "Nothing selected."; //default text
// your rest of the code.
OR 要么
Last check can be done as 最后检查可以完成
selection = selection || "Nothing selected.";
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