[javascript] JavaScript/jQuery - "$ is not defined- $function()" error

I am trying to run a JavaScript/jQuery function and Firebug gets the error:

$ is not defined $(function()".

The JavaScript code is placed inside a file called core.js and referenced by index.php. What causes this error?


<script type="text/javascript">
    var formObject = {
        run : function(obj) {
            if (obj.val() === '') {
                obj.nextAll('.update').html('<option value="">----</option>').attr('disabled', true);
            } else {
                var id = obj.attr('id');
                var v = obj.val();
                jQuery.getJSON('/mod/update.php', { id : id, value : v }, function(data) {
                    if (!data.error) {
                    } else {
                        obj.nextAll('.update').html('<option value="">----</option>').attr('disabled', true);

    $(function() {

        $('.update').live('change', function() {



    <select name="main" id="category" class="update">
    <option value="">Select one</option>

        <? if (!empty($list)) { ?>
            <? foreach($list as $row) { ?>
                <option value="<?php echo $row['id']; ?>">
                    <? echo $row['name']; ?>

            <? } ?>
        <? } ?>


This question is related to javascript jquery

The answer is

You need to include the jQuery library on your page.

You can download jQuery here and host it yourself or you can link from an external source like from Google or Microsoft.


<script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.6.2/jquery.min.js"></script>


<script type="text/javascript" src="http://ajax.microsoft.com/ajax/jquery/jquery-1.6.2.min.js">

This may be useful to someone:

If you already got jQuery but still get this error, check you include jQuery before the js that uses it, specially if you use @RenderBody() in ASP.NET C#

You have to include jQuery before the @RenderBody() if you include the js inside the view that @RenderBody() calls.

Include jquery.js and if it is included, load it before any other JavaScript code.


(function($) {
    $(function() {
        $('.update').live('change', function() {

By using this way you ensure the global variable jQuery will be bound to the "$" inside the closure. Just make sure jQuery is properly loaded into the page by inserting:

<script type="text/javascript" src="http://code.jquery.com/jquery-1.7.1.min.js"></script>

Replace "http://code.jquery.com/jquery-1.7.1.min.js" to the path where your jQuery source is located within the page context.

Im using Asp.Net Core 2.2 with MVC and Razor cshtml My JQuery is referenced in a layout page I needed to add the following to my view.cshtml:

@section Scripts {

if you are trying to use jquery in your electron app before adding jquery you should add it to your modules:

    if (typeof module === 'object') {
        window.module = module;
        module = undefined;
<script src="js/jquery-3.5.1.min.js"></script>

I have solved it as follow.

import $ from 'jquery';

(function () {
    // ... code let script = $(..)