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Check maxlength of multiline textbox in JavaScript

, 21 Feb 2012 CPOL
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This post will help you to resolve problem of checking maxlength of Multiline textbox (Internet Explorer, Chrome & Firefox)

Introduction

ASP.NET provides textbox controls for data inputs and they are used vastly on the websites. TextMode='Multiline' property of textbox is used everywhere to input comments or any large data.

With my program assignment, I came across a problem to set MaxLength for multiline textbox, i.e., after some specified length, the textbox should not accept any characters.

(Note: This solution was only tested & recommended for Internet Explorer (5+), Chrome & Firefox.)

Details

The MaxLength property of textbox control works fine if Multiline mode is not set, but if TextMode='Multiline' is set in aspx page, then this property is of no use and user can input any number of characters inspite of setting maxlength.

Finally, I was able to find a solution and wanted to share it with you all.

This example requires just very basic knowledge of JavaScript, so don’t be scared. I promise this will be one of the easiest JavaScripts that can solve a complex problem.

Add the following to your Multiline box in aspx page:

<asp:TextBox Rows="5" Columns="80" ID="txtCommentsForSearch" 
onkeyDown="return checkTextAreaMaxLength(this,event,'10');" 
onblur="checkLength(this, '10')" TextMode="multiLine" 
CssClass="textArea" runat="server"> </asp:TextBox>        

*txtCommentsForSearch-This is the ASP.NET control that is having multiline property set.

I have used MaxLength='1999', same property you have to use in underlying JavaScript file also. I have also passed this length to the calling JavaScript method, so that in case the MaxLength is not accessible, then it can be picked from parameters of JavaScript method.

In new browser versions, MaxLength of multiline textbox is not accessible in JavaScript, so it's good to assign the required maxlength in JavaScript method calls.

Add the following to your JavaScript file:

// JScript File

function checkTextAreaMaxLength(textBox, e, length) {

            var mLen =  length;
            
            var maxLength = parseInt(mLen);
            if (!checkSpecialKeys(e)) {
                if (textBox.value.length > maxLength - 1) {
                    if (window.event)//IE
                    {
                        e.returnValue = false;
                        return false;
                    }
                    else//Firefox
                        e.preventDefault();
                }
            }
        }

        function checkSpecialKeys(e) {
            
            if (e.keyCode != 9 && e.keyCode != 8 && e.keyCode != 46 && 
            e.keyCode != 35 && e.keyCode != 36 && e.keyCode != 37 && 
            e.keyCode != 38 && e.keyCode != 39 && e.keyCode != 40)
                return false;
            else
                return true;
        }
        function checkLength(textBox, length) {
            var mLen = length;
            
            var maxLength = parseInt(mLen);
            
            if (textBox.value.length > maxLength) {
                textBox.value = textBox.value.substring(0, maxLength);
            }
        }

Note: This implementation is written just to provide a basic and quick help in JavaScript. Nowdays Jquery is preferred and has more easy ways to do things. I myself have moved to Jquery since the past few years. I will post the similar article in Jquery too if anyone is interested.

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

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About the Author

Surjit Singh Dadhwal
Software Developer (Senior)
India India
Programming is my passion and C# is my friend, Javascript is my first crush..
Surprized!!!, don't be....
I love doing programming and writing efficient code, with the help of code project; I am able to share my experiences too with you all.
 
Thanks for visiting and voting this post.. [Smile | :) ]

Comments and Discussions

 
QuestionPaste the text maximum than 10 characters is not working PinmemberUmesh Deshmukh3510-Sep-14 2:04 
AnswerRe: Paste the text maximum than 10 characters is not working PinmemberSurjit Singh Dadhwal23-Sep-14 21:31 
QuestionMARana Pinmemberaxeemg23-Jan-14 21:37 
AnswerRe: MARana PinmemberMember 107868794-May-14 5:24 
GeneralRe: MARana PinmemberSurjit Singh Dadhwal23-Sep-14 21:31 
GeneralMy vote of 3 Pinmemberkiran.puchakayala27-Jun-12 3:55 
GeneralMy vote of 5 Pinmemberbengeorge10-Apr-11 11:19 
GeneralDoes not work if user directly pastes the text from clip board Pinmemberarpitk15-Jan-09 1:04 
GeneralRe: Does not work if user directly pastes the text from clip board PinmemberPaul Lockett23-Aug-10 2:16 
Generalpasting PinmemberStrider699-Sep-08 13:48 
QuestionRe: pasting Pinmemberseth.dhawal21-Dec-08 20:39 
Generalnot cross-browser solution PinmemberADLER119-May-08 11:28 
GeneralRe: not cross-browser solution PinmemberSurjit Singh Dadhwal22-May-08 20:50 
GeneralNeed Proper Formatting before Approve PinmemberAbhijit Jana18-May-08 23:33 
GeneralRe: Need Proper Formatting before Approve PinmemberSurjit Singh Dadhwal22-May-08 20:51 
Formatting corrected.

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