JSFiddle - React, Tailwind, and code Playground

HTML

<input type="file" name="image" class="fileUpload">
<input type="file" name="image" class="fileUpload">
<input type="file" name="image" class="fileUpload">

JavaScript

var fileUpload = document.getElementsByClassName('fileUpload');

for (var i = 0; i < fileUpload.length; i++) {
    fileUpload[i].onchange = function () {
        var filename = this.value;
        var a = filename.split(".");
        if (a.length === 1 || (a[0] === "" && a.length === 2)) {
            return "";
        }
        var suffix = a.pop().toLowerCase();
        //if( suffix != 'jpg' && suffix != 'jpeg' && suffix != 'png' && suffix != 'gif' && suffix != 'tiff'){
        if (!(suffix in {
            jpg: '',
            jpeg: '',
            png: '',
            gif: '',
            tiff: ''
        })) {
            this.value = "";
            alert('Please select an image.');
        }
    }
}