Validation in html not working

I have a filter method implemnted(Django). The filter works based on some choices in drop down and text entered in a text field. Now i wanted to validate the form. I tried doing it like this: But its not getting validated. Can somebody help me to solve this?

<form id="myform" action="http://10.1.0.90:8080/filter/" method="POST" >
    Filter By: 
    <select name="choices" onsubmit="document.forms[0].submit()" style="color: black; background-color: #BDBDBD" >
        <option value="">Select A Choice开发者_运维问答 </option>
        <option value="Name">Name</option> 
        <option value="Designation" >Designation</option>
        <option value="EmployeeID" >EmployeeID</option>
        <option value="Project" >Project</option>
        <option value="DateOfJoin" >Date Of Join</option>   
    </select>
    <input type="text" name="textField" style="color: black; background-color: #BDBDBD" >
    <input type="submit" value="Go" onclick="validator()">
    </form>
    <script type="text/javascript">
    function validator(){   
        if (document.getElementById('Designation').value == "")
        {
            alert("Enter a value");
        }
    }
    </script>

I have build a demo at http://jsbin.com/ayuzi4/

Check if it helps.

The changes are

<select name="choices" onsubmit="document.forms[0].submit()" style="color: black; background-color: #BDBDBD" >

is

<select name="choices" id="choices" style="color: black; background-color: #BDBDBD" >

And

 <input type="submit" value="Go" onclick="validator()">

is now

 <input type="submit" value="Go" onclick="return validator();">

and the new js function is

function validator(){   
    if (document.getElementById('choices').value === "")
    {
        alert("Enter a value");
        return false;
    }
}

if (document.myform.getElementById('Designation').value == "")   
and add  
    return false;  
    } else {  
        return true;  
    }  

not sure....try this

Look closely at your code and try and understand what the various Javascript functions are doing.

On the submit button, you have a function that calls the validator. But on the select box itself, you have a function that submits the form! So as soon as you click the select box, the form will be submitted, so the validator function is never called.