Question

As title which of them is better and why? Any weaknesses from doing it?
I been hearing that Jquery/Javascript checking is bad and adviced to use PHP but somehow don’t know why….

Need some recommend from any of you. Thanks in advance.

Anyone see if this is good or bad:

<input type="file" name="task_doc" class="task_doc"  onChange="checkext();"/>

function checkext(){
var permittedFileType = ['pdf', 'doc', 'docx', 'xls', 'xlsx'];
var fext = $(".task_doc").val().split('.').pop().toLowerCase();
var resultFile = validate_filetype(fext, permittedFileType);
    if(resultFile === false){
         $(".task_doc").replaceWith("<input type='file' name='task_doc'    class='task_doc'  onChange='checkext();'>");
        alert("Invalid Extension");

    }
    else{
        alert("Success");
    }
}

function validate_filetype(fext, ftype)
{
    for(var num in ftype)
    {
        if(fext == ftype[num])
            return true;
    }

    return false;
}

Answer 1

If you use only javascript to check for data-validity, advanced users will have the possibility of uploading any data they want.

On the other hand using javascript might be a convenient way for the user to get fast feedback, if his entered data (files in this case) is invalid.

So I suggest using both client side and server side scripts.