JavaScript checks whether the textarea value is null and provides the corresponding prompt, javascripttextarea

JavaScript checks whether the textarea value is null and provides the corresponding prompt, javascripttextarea

In webpage design, JavaScript is often used to determine whether a user inputs valid data. If the user does not input data, a prompt is displayed. How can this problem be determined? This section describes how to use JavaScript to determine whether the textarea value is null.

The JavaScript function is provided below:

If (document. getElementById ("htmer"). value = '') {alert (" Enter the content! "); Return false ;}

Note that the red part in the above Code is '= '', which is a single quotation mark instead of a double quotation mark, which can reduce unnecessary troubles.

How does javascript determine that textarea is empty?

It cannot only be a Null String ""
Null

Document. form1.textarea name. value = "" | document. form1.textarea name. value = null

In JSP webpage design, how can I determine whether the value of <textarea> is null?

This indicates the current object. Your this does not represent your textare. You can give textare an id and then call var obj = document in the check () method. getElementById ("XX"); in this way, the textare tag is obtained and obj is determined in the check method. value = "", as follows:

<Script type = "text/javascript">
Function check (){
Var obj = document. getElementById ("experimentnote ");

If (obj. value = "")
{
Alert ("the input format of the experiment record is incorrect. Please enter it again! ");
Obj. focus ();
Return false;
}
</Script>
The textarea statement is as follows:
<Form name = "form1" action = "AddStep2.jsp" method = "post" onsubmit = "return check () "> <textarea name =" ExperimentNote "ROWs =" 10 "COLS = 30 id =" experimentnote "> </textarea> </form>