File type validation with Javascript

Question

I have a question regarding to JavaScript validation. I am validaing the whenever my scripts runs, it validates but also the action

Answer 1

var _URL = window.URL || window.webkitURL;
    $("input[type=file]").change(function(e) {
        var file;
            if ((file = this.files[0])) {
                var img = new Image();
                img.onload = function () {
                    // do to on load
                };
                img.onerror = function () {
                    alert("valid format " + file.type);
                };
                img.src = _URL.createObjectURL(file);
            }
    });

Answer 2

File Extension Validation through javascript

function ValidateExtension() {
        var allowedFiles = [".doc", ".docx", ".pdf"];
        var fileUpload = document.getElementById("fileUpload");
        var lblError = document.getElementById("lblError");
        var regex = new RegExp("([a-zA-Z0-9\s_\\.\-:])+(" + allowedFiles.join('|') + ")$");
        if (!regex.test(fileUpload.value.toLowerCase())) {
            lblError.innerHTML = "Please upload files having extensions: <b>" + allowedFiles.join(', ') + "</b> only.";
            return false;
        }
        lblError.innerHTML = "";
        return true;
    }

onclick event of submit button call this javascript function.

With the help of ID = lblError , print the error message in html section.