javascript 如何检查 document.getElementbyId 中包含空值或未定义值？
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时间：2020-10-27 07:29:49 来源:igfitidea点击:
how to check document.getElementbyId contains null or undefined value in it?
提问by Matrix
if(typeof (document.getElementById("courseId").value!=="undefined") || document.getElementById("courseId").value!==null)
{
Courseid = document.getElementById("courseId").value;
}
回答by Marco Forberg
rewrite it that way:
这样重写：
if(document.getElementById("courseId") && document.getElementById("courseId").value)
{
CourseId = document.getElementById("courseId").value;
}
回答by glosrob
If you explicitly want to check for undefined and null you can do
如果你明确想要检查 undefined 和 null 你可以做
if(document.getElementById('courseId') === null ||
document.getElementById('courseId') === undefined) {
//logic
}
回答by Eric
An input's value will never be nullor undefined - it will be the empty string, "".
输入的值永远不会是null或未定义的——它将是空字符串"".
