JavaScript function giving Uncaught reference error while getting the value of text box

Question

I am trying make textbox blank and set focus on it using Java Script.
I used following code for that

document.getElementById("textmob")="";
document.getElementById("textmob").focus;

But I get following error:

Uncaught ReferenceError: Invalid leftend side assignment;

My Html Code

<asp:TextBox ID="mob" runat="server" CssClass="text" AutoPostBack="True" onchange = "validateMob(this)" ></asp:TextBox>

My validation function

 function validateMob(txtmob)

          {
            debugger;
            var rx = /^\d{10}$/;

           if (!txtmob.value.match(rx)) {
               alert('Invalid Mobile No');
               // document.getElementById("mob") = "";
              document.getElementById("mob").focus();
            }
        }

http://stackoverflow.com/questions/14028959/why-does-jquery-or-a-dom-method-such-as-getelementbyid-not-find-the-element — Quannt, Oct 21 '13 at 07:22

score 2 · Answer 1 · answered Oct 21 '13 at 07:16

2

You can't just set it to "".

document.getElementById('textmob')

gives you the element itself.

In order to set the content of the element to "",

use .value.

document.getElementById("textmob").value="";

answered Oct 21 '13 at 07:16

Se Won Jang

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I tried it but it gives uncaughtTypeError: can not set property value to null – ashish kumar Oct 21 '13 at 07:19

score 2 · Answer 2 · edited Oct 21 '13 at 07:26

2

This is invalid assignment:

document.getElementById("textmob")="";

You are trying to assign a string object to a JavaScript element. I guess .value is missing.

edited Oct 21 '13 at 07:26

Navnath Godse

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answered Oct 21 '13 at 07:17

Aryan

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Sergio · Accepted Answer · 2013-10-21T07:25:55.473

1

I think you forgot to use .value and () in foucus()

Try this:

document.getElementById("textmob").value = "";
document.getElementById("textmob").focus();

Fiddle

edited Oct 21 '13 at 07:25

answered Oct 21 '13 at 07:16

Sergio

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Is it Working in .net aspx textbox control. – ashish kumar Oct 21 '13 at 07:26
@ashishkumar, please post your html also. – Sergio Oct 21 '13 at 07:27
I made textbox autopostback property true – ashish kumar Oct 21 '13 at 07:27
– ashish kumar Oct 21 '13 at 07:28
@ashishkumar, and how does that validate function look like? (post in your question) – Sergio Oct 21 '13 at 07:33
@ashishkumar, check this http://stackoverflow.com/questions/5039544/getting-textbox-value-in-javascript – Sergio Oct 21 '13 at 07:35

score 1 · Answer 4 · answered Oct 21 '13 at 07:27

1

Its just a minor mistake in your syntax it should be like that

document.getElementById("textmob").value="";
document.getElementById("textmob").focus();

check complete example

<html>
<head>
<script>
function my()
{
        document.getElementById("textmob").value="";
        document.getElementById("textmob").focus();
}
</script>
</head>
<body>

<input id="k" type="text">
<input id="textmob" type="text">

<button onclick="my()" id="b" value="Click ME">


</body>
</html>

answered Oct 21 '13 at 07:27

Achilles

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i call javascript function on onchange event of text box – ashish kumar Oct 21 '13 at 07:32
do you want to call that function on every keypress event in that textbox or when user has entered all the text? – Achilles Oct 21 '13 at 07:40
onlost focus of textbox – ashish kumar Oct 21 '13 at 07:40
Try onblur function – Achilles Oct 21 '13 at 07:48

score 0 · Answer 5 · answered Oct 21 '13 at 07:19

0

try:

 document.getElementById("textmob").focus(function() {
      *do what you like with text field*;
    });

answered Oct 21 '13 at 07:19

Lucky Lefty

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1
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JavaScript function giving Uncaught reference error while getting the value of text box

5 Answers5

Fiddle