内联Javascript有效，但在外部不起作用
[英]Inline Javascript works, but doesn't work externally
问题描述
I am fairly new to JavaScript and I was wondering if anyone can help me with this problem. 
我对JavaScript相当陌生，我想知道是否有人可以帮助我解决这个问题。 I have three text boxes, and the first two show first and last name. 我有三个文本框，前两个显示名字和姓氏。 And I want the last textbox to contain both first and last. 我希望最后一个文本框同时包含第一个和最后一个。
Here's the code: 这是代码：
<!doctype html>
<html>
<head>
<title>Javascript Textbox</title>
</head>
<body>
First Name: <input id="fname" type="text" value="John"><br>
Last Name: <input id="lname" type="text" value="Smith"><br>
<input id="textbox" readonly>
<button onclick="textbox.value=fname.value+' '+lname.value">press to see full name</button>
<script type="text/javascript" src="testing.js"></script>
</body>
</html>
This works fine, but when I try to use an external file, testing.js and switching onclick="testFunction()" , it doesn't work anymore. 这可以正常工作，但是当我尝试使用外部文件testing.js并切换onclick="testFunction()" ，它将不再起作用。
testing.js: testing.js：
function testFunction() {
var first = document.getElementById("fname").value;
var last = document.getElementById("lname").value;
var textb = document.getElementById("textbox").value;
textb = first + " " + last;
}
3 个解决方案
解决方案1
1 已采纳 2014-12-19 00:39:58
http://jsfiddle.net/1vshky4s/ http://jsfiddle.net/1vshky4s/
Ultimately your problem is that you are assigning the texb var the value of the text box, then overriding it with a concatenated string, then doing nothing at all with the results. 最终，您的问题是要为texb var分配文本框的值，然后使用串联字符串覆盖它，然后对结果完全不执行任何操作。
function testFunction()
{
var first = document.getElementById("fname").value;
var last = document.getElementById("lname").value;
var textb = first + " " + last;
document.getElementById("textbox").value = textb;
}
actually do something with the textb var and you should be good to go. 实际使用textb var做些事情，您应该一切顺利。 Check the fiddle. 检查小提琴。
解决方案2
1 2014-12-19 00:46:07
change your function to 将功能更改为
function testFunction() {
var first = document.getElementById("fname");
var last = document.getElementById("lname");
var textb = document.getElementById("textbox");
textb.value = first.value + " " + last.value;
}
解决方案3
-1 2014-12-19 00:33:17
Move: 移动：
<script type="text/javascript" src="testing.js"></script
Into the head of page. 进入页面head 。 You try to bind function, than doesn't exist. 您尝试绑定功能，但不存在。 script will be loaded after dom. script将在dom之后加载。
ps Or use 'onload' event if window pss ps或如果window pss使用'onload'事件
Here correct function: 这里正确的功能：
function testFunction()
{
var first = document.getElementById("fname").value;
var last = document.getElementById("lname").value;
var textb = document.getElementById("textbox"); //!
textb.value = first + " " + last; // here was error
}
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