这段代码中有什么错误? [英] what is mistake in this code ?
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问题描述
这段代码有什么错误......点击按钮后没有任何反复发生..
< html >
< head >
< script >
function change()
{
var t = document .getElementById( text1 中跨度>);
if (t.value!= )
windows.alert( 您输入了: + t。值);
else
windows.alert( 你会输入一些文字吗);
}
< < span class =code-leadattribute> / script >
< / head >
< body >
< 输入 type = text id = text1 >
< 输入 类型 = 按钮 名称 = b1 value = click me onclick = change(); >
< / body >
< / html >
解决方案
功能变更(){
var t = document.getElementById( text1 中跨度>);
if (t。 value != )
alert( 您输入了: + t。 value );
else
alert( 你会输入一些文字);
}
你所拥有的甚至不是有效的javacript。你应该得到一本关于js的书,至少要学习基础知识,因为这不是学习不断要求人们修复你的基本错误的好方法。
这个bug是 lexical :在中你会输入一些文字
,缺少右引号。
这样的错误不能甚至通过处理异常直接捕获。在我的文章的这一章中解释了捕获它们作为例外的方法: JavaScript Calculator, 5。处理词汇错误 。
此外,您的代码几乎没有实际意义:如果输入,则认为输入为空。如何输入真空字符串,零长度?两个或多个空白字符怎么样?
为了改善这一点,你可以使用字符串函数.trim()
:
https:// developer。 mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/Trim [ ^ ]。
-SA
What is the mistake in this code... upon clicking the button nothing happens..
<html>
<head>
<script>
function change()
{
var t= document.getElementById("text1");
if (t.value!=" ")
windows.alert ("You entered: "+t.value);
else
windows.alert("would you enter some text);
}
</script>
</head>
<body>
<input type= "text" id="text1">
<input type ="button" name = "b1" value = "click me" onclick ="change();">
</body>
</html>
解决方案
function change() { var t = document.getElementById("text1"); if (t.value != "") alert("You entered: " + t.value); else alert("would you enter some text"); }
what you had wasn't even valid javacript. You should get a book on js and at least learn the basics as it's not a good way to learn to constantly ask people to fix your basic errors.
The bug is lexical: in"would you enter some text"
, right quotation mark is missing.
Such bugs cannot be caught directly even by handling exceptions. The way to catch them as exception is explained in this chapter of my article: JavaScript Calculator, 5. Handling Lexical Errors.
Also, your code makes little to no practical sense: you consider input as "empty" only if " " is entered. How about entering "real empty" string, zero-length? how about two or more blank characters?
To improve this, you could use the string function.trim()
:
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/Trim[^].
—SA
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