Javascript 为什么 string.length 返回未定义？
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why string.length return undefined?
提问by pierrotlefou
In the popup window, selText does have the value "great," but the length is always undefined. Something related with the encoding of the string?
在弹出窗口中，selText 确实具有值“great”，但长度始终为undefined。与字符串编码有关的东西？
var selText = document.getSelection(); //suppose "great" is selected
alert( "selected ->" + selText + " len is " + selText.length);
回答by user113716
Because you're getting a DOM selection object instead of a String. To get the text, call toString().
因为你得到的是一个 DOM 选择对象而不是一个字符串。要获取文本，请调用toString()。
var selText = document.getSelection().toString();
The reason the string successfully shows up in the alert, is that the concatenation causes an implicit toString()to occur.
字符串成功显示在警报中的原因是连接导致隐式toString()发生。
回答by John K
The MDN documentationstates.
该MDN文档的状态。
In the above example, selObj is automatically "converted" when passed to window.alert. However, to use a JavaScript String property or method such as length or substr, you must manually call the toString method.
-- https://developer.mozilla.org/en/window.getSelection
在上面的例子中，selObj 在传递给 window.alert 时会自动“转换”。但是，要使用 JavaScript 字符串属性或方法（例如 length 或 substr），您必须手动调用 toString 方法。
-- https://developer.mozilla.org/en/window.getSelection
It's suggesting you call document.getSelection().ToString().length;
建议你打电话 document.getSelection().ToString().length;
回答by The Mask
Deprecated method document.getSelection() Try use window.getSelection().
不推荐使用的方法 document.getSelection() 尝试使用 window.getSelection()。
var selText = window.getSelection().toString();
if(selText)
{
alert( "selected ->" + selText + " len is " + (selText.length - 1));
}
