JSFiddle - React, Tailwind, and code Playground
HTML
<form id="file_upload" action="">
<input type="file" id='file' name="datafile">
<input type="submit" value="submit"/>
</form>
JavaScript
$('#file').change(function(e) {
var file = $(this).val();
var ext = file.split('.').pop();
alert(ext);
if(ext=='jpg'){
alert('correct file');
}else{
alert('wrong file');
return false;
}
});