Open file-upload.js file (assets/js/file-upload.js) You can see below js
$(document).on('change', '.file-browserinput', function() {
var input = $(this),
numFiles = input.get(0).files ? input.get(0).files.length : 1,
label = input.val().replace(/\\/g, '/').replace(/.*\//, '');
input.trigger('fileselect', [numFiles, label]);
});
// We can watch for our custom `fileselect` event like this
$(document).ready( function() {
$(':file').on('fileselect', function(event, numFiles, label) {
var input = $(this).parents('.input-group').find(':text'),
log = numFiles > 1 ? numFiles + ' files selected' : label;
if( input.length ) {
input.val(log);
} else {
if( log ) alert(log);
}
});
});