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Jul 08

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Javascript Validate Field Name

Here is a simple tutorial on how to use Javascript to validate a form field name. In this tutorial I will show how to display the error next to the name field instead of the error message is displayed using the alert function. The error will be displayed indicating that no name the name field (I use a username field, however, the code can be applied to a field name) in the region of error when the user clicks the button send. When the user enters a name in the name field and then re-submit the error has been shown.

Here is the HTML form:

name form <= "register" method = "POST" action = "connect2.php" onsubmit = "return checkWholeForm (this)">
<fieldset>
<div id="usernameField"> label <style = "padding-left: 20px;" to = "user" username>: </ label> <input type = "text" name = "username" id = "username" size = "30" MaxLength = "45" / span> <id = "errorMesUsername"> </ span> </ div>
<div> label style <= "padding-left: 20px;" to = "pass" password>: </ label> <input type = "password" name = "pass" id = "pass" size = "30" MaxLength = "45" /> </ div>
the < for = "email-mail>: </ label> <input type =" text "name =" email "id =" email "size = "30" MaxLength = "45" /> <br />
</ Fieldset>
<Input type = "submit" value = "submit" name = "submit" />
</ Form>

Basically, when the user clicks the submit button the browser expects a value Return on checkWholeForm () function. The word "this" refers to the form as it is an object. In other words, "This object is the shape. Notice There is a section side span input field is the username.

<span id="errorMesUsername"> </ span>

There is nothing is displayed the user name when the form is opened as this is where the JavaScript will return the error message if no name entered in the field.

VALIDATE HOW TO USE THE JAVASCRIPT FUNCTION

This is the JavaScript function to checkWholeForm ():

checkWholeForm function (theForm) (with (theForm) (CheckUsername (username.value)) return true;)

Note the above uses a Javascript () function. All this is saying is that all properties within the braces () use the 'theForm' object. In other words, this "username" is the property of 'theForm' object. The 'username' is the value of the attribute 'name' in the input tag as follows:

Input <type = "Text" name = "username" id = "username" size = "30" MaxLength = "45" />

If you choose not to use the with () function, we could write the checkWholeForm (theForm) as follows;

checkWholeForm function (theForm) (
checkUsername (theForm.username.value)
return true;
)

If we were to create additional validation, as for the password field and use of with () function, we could write the checkWholeForm (theForm) as follows:

checkWholeForm function (theForm) (
with (theForm) (
checkUsername (username.value)
checkPassword (pass.value)
)
return true;
)

The 'pass.value "Is to pass the value of the input the password field to checkPassword () function. The" approved "is the value of the attribute 'name' the 'input tag. This function is incomplete, since it will ultimately be the validation of the password using PREG (Perl regular expressions).

checkUsername function (UsernameVal) (
this.errorMes = document.getElementById ("errorMesUsername");

var error = "";
if (usernameVal == "") (
error = "You did not enter a username.n"
this.errorMes [deleted] = error;
) Else if (this.errorMes [deleted]! = "") (
this.errorMes [deleted] = "";
Else ()
return true;
)
)

Show error message if you enter NO NAME

The first line with 'this.errorMes "is simply the creation of a local variable. You can create a variable as "errorMes var 'instead. I can set mainly in PHP I am used to using the term" this " referring to objects. We are receiving the item by the id value. In other words, the id attribute of the SPAN tag "has a value of 'errorMesUsername. The label span as you will notice immediately after the user input label field. This is where the error is displayed if the user has not entered any value in the user field. The reference to the DOM are later used in sentences.

Then in the next line do the variable error "Like anything in case there is a previous value attached to it. Then we check for some conditions. Since this function (ie checkUsername ()) is checking to see if the user has entered the text of the first conditional statement is "if (== usernameVal "")". Do not forget to equality marriage (ie, signs'==') of conditional statements. This is different to assign a value to the variable where you only need an equal (ie '=') sign. If it appears that the user has not entered any text in the username field and then assign the value of the variable "error" equals "You username.n has not entered an "that is placed inside the span tag (ie, innerHTML) where the id attribute is equal to 'errorMesUsername.

DELETE Error message if name is entered

The second conditional "else if (this.errorMes.innerHMTL! =" ")" You are checking to see if there is any value within the span tag. In other words, if there are any errors shown. We need this condition when the user enters a name in the field after read the error message and then resubmit the form. To explain further, if the condition "UsernameVal ==" "false statements or, in other words, if there is now a text that was entered by the user in the name field and then move to the next conditional, which is where we are. Since there is a text entered in the name field we need to check to see if there is an error appearing on the labels of adjustment and if there is then we have to remove (ie, not shown). We To do this, assign the value of the label span equal to nothing with this line "this.errorMes [deleted] =" "'.

As a precaution Additional might have written this' else if 'condition' else if (this.errorMes [deleted]! = "" & & usernameVal = "")'.! The two signs are a new condition to be met. "UsernameVal! =" "It means that if the variable 'usernameVal' is not equal to nothing, or more simply, if the variable 'usernameVal' is equal to something (ie some text was added to the field name). Double negative is equal to a positive.

Just as a note, we could have used onchange JavaScript function () instead of using this sentence. OnChange () check function if the user starts to write anything in the name field. As soon as the user types a text, then we can return another function value based on what the user begins typing.

The last 'other' conditional is simply a catch in the case of the other conditions do not go for any reason whatsoever.

So all the JavaScript code looks like:

checkWholeForm function (theForm) (

with (theForm) (
checkUsername (username.value)
)

return true;
)

checkUsername function (usernameVal) (
this.errorMes = document.getElementById ("errorMesUsername");

var error = "";
if (usernameVal == "") (
error = "It has introduced a username.n"
this.errorMes [deleted] = error;
) Else if (this.errorMes [deleted]! = "") (
this.errorMes [deleted] = "";
) Else (
return true;
)
)

This is a basic example of Javascript validating a name field. Let's go further validation controls to the form fields in the next tutorials.

About the Author

Javascript Tutorial, tips, guides. Victor Kimura
Javascript Tutorial Javascript Validate Name Field

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