JAVASCRIPT

Developing a simple validation library in JavaScript

This series of articles mainly lists some of the most commonly used JavaScript functions for client side validation of HTML forms. You can reuse these scripts to inject into server side controls easily.

Author Info:

By: Jagadish Chaterjee

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February 15, 2006

TABLE OF CONTENTS:

<html>
<head>
    <script id=clientEventHandlersJS language=javascript>
    
    </script>
</head>
      <body>
            <form id="form1">
                  Enter name:<input type="text" id="txtName"> <input type="button" value="Validate" id="Button1" name="Button1" onclick="return Button1_onclick()">
            </form>
      </body>
</html>

Within the above code, I mainly created a simple text box and a button. The textbox is named “txtName” and the button is named “Button1”. The button is defined with an “onclick” event, which calls a JavaScript function named “Button1_onclick”, which is defined as follows:

function Button1_onclick() {
var v = document.all("txtName").value;
alert(isBlank(v));
}

The above function defines a variable “v”, which is assigned with a value available (or typed) in the textbox called “txtName”. The same variable is passed as a parameter to another JavaScript function, “isBlank” (which is defined as follows). The value returned by the function “isBlank” is finally displayed in the form of a message box, using an “alert” statement. Now, let us look into the “isBlank” function.

function isBlank(val){
      if(val==null){return true;}
      if(val.length==0) {return true;}
      return false;
      }

The above function simply accepts any value (as a parameter value) into the variable “val”. The first “if” statement in the function “isBlank” simply checks for “null”. The second “if” statement in the same function counts the number of characters available. If no characters are found, it returns “true”. Finally, if none of the “if” statements work, we return “false” (similar to “not blank”).

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