How to add validation in my own module?

Question

I select the document type from the select option then upload the file so how to validate in the code

<form name="file_up_form" method="post" name="fileupload" enctype="multipart/form-data">
    <div class="field_container1 thumbnail span3">
        <label for="select_option">Select option here</label>
        <select name="doc_type" id="select_option" style="width: 200px;" multiple>
            <option value="1">Education</option>
            <option value="2">Certification</option>
            <option value="3">Client Paperwork</option>
            <option value="4">Invoice</option>
        </select>
    </div>
    <div class="field_container thumbnail span4">
        <label for="file">Upload here: </label>
        <input type="file" name="file" id="file">
        <input class="btn btn-primary" type="submit" value="submit" name="submit">
    </div>
    <input type="hidden" name="check" value="1">
</form>

Here is the validation code I'm using so far:

<script> 
    function validate() 
    { 
        if(document.fileupload.doc_type.value == "" && document.fileupload.doc_type.value == null) 
        { 
            alert( "Please provide your document!" ); 
            return false; 
        } 
        if(document.fileupload.file.value == "" && document.fileupload.file.value == null) 
        {   
            alert( "Please provide your file!" ); 
            return false; 
        } 
        return true; 
    } 
</script>

Answer 1

Change document.fileupload.doc_type.value to document.getElementById('file').value. Also, you're checking if the value is "" AND null, I'm not sure if that is possible.

Unless you need to verify the file format etc., try something simpler like this:

HTML

<form onsubmit="return(validate());" name="file_up_form" method="post" name="fileupload" enctype="multipart/form-data" >
    <div class="field_container1 thumbnail span3">
        <label for="select_option">Select option here</label>
        <select name="doc_type" id="select_option" style="width: 200px;" multiple>
            <option value="1">Education</option>
            <option value="2">Certification</option>
            <option value="3">Client Paperwork</option>
            <option value="4">Invoice</option>
        </select>
    </div>
    <div class="field_container thumbnail span4">
        <label for="file">Upload here: </label>
        <input type="file" name="file" id="file">
        <input class="btn btn-primary" type="submit" value="submit" name="submit">
    </div>
    <input type="hidden" name="check" value="1">
</form>

JavaScript

<script> 
    function validate() 
    { 
        if(!document.getElementById('file').value) 
        { 
            alert( "Please provide your document!" ); 
        } 
        return false; 
    } 
</script>

Shouldn't you also return false (not true as you currently do) if no file is selected to stop the form from being submitted? The <form> tag should probably include an action parameter too.