From the May 2008 Issue of Prestwood eMag

JavaScript Coding Tasks: Checking if a field is blank By Mike Prestwood

Posted 21 years ago on 3/20/2003 and updated 11/7/2008 Take Away: How to validate form field is blank or not using JavaScript.  Tags: javascript , validate , blank , check if field is blank KB100191

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For this example we'll use the document object model to check a checkbox.

Key Points

• Name the form (in this first example, we named the form Example1. You do this so you can use dot notation to refer to "theForm.theField.value".
• Text objects have value property you can use to check.
• You can add an onClick JavaScript event to the form. In this case, we used the event to call a function.

Here's the function code :

function CheckFieldBlank() {

if (Example1.Field1.value == ""){

alert("It's Blank!");

} else { alert("It's not blank.");

};

Here's the form code:

    

    
 

    

    
  onclick="CheckFieldBlank();">

    

   

Checking if a field has a specific value

One more example. This example show how to check for a specific value. In this case we  check for the value 'Mike' in the field.

Here's the function:

function CheckFieldMike() {

if (Example2.Field1.value == "Mike"){

alert("It's Mike!");

} else { alert("It's not Mike.");

};

Here's the form code:

    

    
 

    

    
value="Check If Blank" onclick="CheckFieldMike();">

    

   

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