Question

I take a file via a form , and ask to validate its type. but it sounds the java script doesn’t work or the invoke is not seen ?

<form enctype="multipart/form-data" action="Upload2.jsp"
 method="post" onsubmit="javascript:return validate();">
    <td><b>Choose txt file To Upload:</b></td>
    <td><input name="file" type="file"></td>
    <td><input type="submit" value="Upload File" ></td>
</form>

And here’s the script:

<script language="JavaScript">
    function validate(){
        if(document.form.file.value == "" ) {
            alert("Enter course code !");
            return false;}

        else {
            var value = document.form.file.value;
            var ext = value.substr(dot, value.length);
            //ext = value.slice(file.indexOf(".")).toLowerCase();
            if ( ext=="txt" ) {
                return true; }
            else{
                alert("choose a .txt file");
                return false;}
            }
       }
</script>

And this is the form..
tho i am not sure of my script correctness?

Answer 1

You can capture what’s after the last period in a string using:

ext = value.split(".").pop();

---

You take your String value split it into an array:

var myValue = "some.thing.ext";

var myArray = myValue.split(".");

now myArray is:

["some", "thing", "ext"];

You can now pop the last value from the array using .pop().

var ext = myArray.pop();

now

ext === "ext";
myArray === ["some", "thing"]

---

in context:

function validate(){
    if(document.form.file.value == "" ) {
        alert("Enter course code !");
        return false;}

    else {
        var value = document.form.file.value,
            ext = value.split(".").pop();
        if ( ext == "txt" ) {
            return true; }
        else{
            alert("choose a .txt file");
            return false;}
        }
   }

If you change your onsubmit to:

onsubmit="javascript:return validate(this);"

Then you will get the form element as first argument in value:

function validate(form){
    var value = form.file.value,
        ext = value.split(".").pop();

    if( !value ) {
        alert("Enter course code !");
    }
    else if ( ext !== "txt" ) {
        alert("choose a .txt file");
    }

    return ( ext === "txt" );
}

---

NOTE:

Never use javaScript as your only validation. Use some sort of server-site language to determinate if the validation is passed.

Use JS to make i more slick for the user to operate on your site.