JavaScript > 如果我设置“var x = document.getElementById('inputText').value”并更新“x”，为什么值不更新？
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JavaScript > If I set "var x = document.getElementById('inputText').value" and I update "x", why doesn't the value update?
提问by sapiensgladio
In the following example, why doesn't the "value" of the input "test" update to "second"?
在下面的示例中，为什么输入“test”的“value”没有更新为“second”？
<html>
<head>
<script type="text/javascript">
getText = function() {
var test = document.getElementById('test').value;
test = "second";
//note: if you insert "alert(test)" it returns "second"
}
</script>
</head>
<body>
<label for="test">Test </label><input type="text" id="test" value="first" onclick="getText()"></input>
</body>
</html>
回答by Jared Farrish
Because Javascript assigned x as a value and not a reference to the original object.
因为 Javascript 将 x 分配为一个值而不是对原始对象的引用。
For example, you could instead:
例如，您可以改为：
function setText(x) {
document.getElementById('test').value = x;
}
getText = function() {
return document.getElementById('test').value;
}
And the value you set with setText()will be reflected by getText(), since getText()will also use the reference object's value, and not a copy of the value.
并且您设置的值setText()将由 反映getText()，因为getText()还将使用引用对象的值，而不是该值的副本。
EDIT
编辑
As Bryan points out, this would be a copy by reference with a global scope:
正如 Bryan 指出的，这将是一个具有全局范围的引用副本：
var test = document.getElementById('test');
function setText(x) {
test.value = x;
}
getText = function() {
return test.value;
}
The original testvariable stores a reference to the element, not a value associated with an attribute of the element.
原始test变量存储对元素的引用，而不是与元素属性关联的值。
回答by Guffa
You are copying the value to a variable. Changing the variable won't change the original, because the variable just contains a copy.
您正在将值复制到变量。更改变量不会更改原始变量，因为变量只包含一个副本。
If you store the reference of the element in the variable, you can use that to set the value:
如果将元素的引用存储在变量中，则可以使用它来设置值：
var test = document.getElementById('test');
test.value = "second";
回答by BalusC
You're assigning the element's value to a variable and then changing the variable. This is not reflected back in the element's value. You need to change the element's value instead.
您将元素的值分配给一个变量，然后更改该变量。这不会反映在元素的值中。您需要改为更改元素的值。
document.getElementById('test').value = "second";
回答by Blender
Because you're setting the valueof testto be the string document.getElementById('test').value.
因为你设置值的test为字符串document.getElementById('test').value。
You aren't linking the two together.
你没有将两者联系在一起。
If you are looking to do that, you can use a function:
如果你想这样做，你可以使用一个函数：
function test(x) {
document.getElementById('test').value = x;
}
test('foo');
In Python, you can do this. In JavaScript, I don't think so.
在 Python 中，你可以做到这一点。在 JavaScript 中，我不这么认为。
回答by locrizak
because
因为
document.getElementById('test').valueis a getter where as
是一个吸气剂，作为
document.getElementById('test').value = "second"is a setter
是一个二传手
回答by kafuchau
test = document.getElementById('test').value;
...only gives you a copy of the value at that instant. When you modify test, you need to put that back into input field you'd like to change:
...只为您提供那个瞬间的值的副本。当您修改 时test，您需要将其放回您想要更改的输入字段中：
var test_input = document.getElementById('test');
test_input.value = "second";
回答by Richard Schneider
Setting the local variable testto "second" will do nothing. I assume you want getText to update the DOM. Try this:
将局部变量设置test为“second”将什么也不做。我假设您希望 getText 更新 DOM。尝试这个：
getText = function() { document.GetElementById('test').value("second"); }
回答by Drew
Point to element instead of value: http://jsbin.com/axufi4/edit
指向元素而不是值：http: //jsbin.com/axufi4/edit
回答by tomfumb
Although javascript ultimately treats everything as an object, I believe only arrays and objects are passed by reference. Strings, ints and floats are passed by value.
尽管 javascript 最终将一切都视为对象，但我相信只有数组和对象是通过引用传递的。字符串、整数和浮点数按值传递。
Text inputs will always give you a string (even if you restrict input to numbers)
文本输入将始终为您提供一个字符串（即使您将输入限制为数字）
回答by mrtsherman
<script type="text/javascript">
getText = function() {
var test = document.getElementById('test').value;
test = "second";
//note: if you insert "alert(test)" it returns "second"
document.getElementById('test').value = test;
}
</script>
