$ is not a function - jQuery error

I have the jQuery loaded fine, I've quadruple-checked, though I'm getting this error in FireBug "$ is not a function" and my code doesn't work.

Here's my code:

<script type="text/javascript">
    $("ol li:nth-child(1)").addClass('olli1');
    $("ol li:nth-child(2)").addClass("olli2");
    $("ol li:nth-child(3)").addClass("olli3");
    $("ol li:nth-child(4)").addClass("olli4");
    $("ol li:nth-child(5)").addClass("olli5");
    $("ol li:nth-child(6)").addClass("olli6");
    $("ol li:nth-child(7)").addClass("olli7");
    $("ol li:nth-child(8)").addClass("olli8");
    $("ol li:nth-child(9)").addClass("olli9");
    $("ol li:nth-child(10)").addClass("olli10");
    $("ol li:nth-child(11)").addClass("olli11");
    $("ol li:nth-child(12)").addClass("olli12");
    $("ol li:nth-child(13)").addClass("olli13");
    $("ol li:nth-child(14)").addClass("olli14");
    $("ol li:nth-child(15)").addClass("olli15");
    $("ol li:nth-child(16)").addClass("olli16");
    $("ol li:nth-child(17)").addClass("olli17");
    $("ol li:nth-child(18)").addClass("olli18");
    $("ol li:nth-child(19)").addClass("olli19");
    $("ol li:nth-child(20)").addClass("olli20"); 
</script>

In Wordpress jQuery.noConflict() is called on the jQuery file it includes (scroll to the bottom of the file it's including for jQuery to see this), which means $ doesn't work, but jQuery does, so your code should look like this:

<script type="text/javascript">
  jQuery(function($) {
    for(var i=0; i <= 20; i++) 
      $("ol li:nth-child(" + i + ")").addClass('olli' + i);
  });
</script>

It's really hard to tell, but one of the 9001 ads on the page may be clobbering the $ object.

jQuery provides the global jQuery object (which is present on your page). You can do the following to "get" $ back:

jQuery(document).ready(function ($) {
    // Your code here
});

If you think you're having jQuery problems, please use the debug (non-production) versions of the library.

Also, it's probably not best to be editing a live site like that ...

<script type="text/javascript">
    $("ol li:nth-child(1)").addClass('olli1');
    $("ol li:nth-child(2)").addClass("olli2");
    $("ol li:nth-child(3)").addClass("olli3");
    $("ol li:nth-child(4)").addClass("olli4");
    $("ol li:nth-child(5)").addClass("olli5");
    $("ol li:nth-child(6)").addClass("olli6");
    $("ol li:nth-child(7)").addClass("olli7");
    $("ol li:nth-child(8)").addClass("olli8");
    $("ol li:nth-child(9)").addClass("olli9");
    $("ol li:nth-child(10)").addClass("olli10");
    $("ol li:nth-child(11)").addClass("olli11");
    $("ol li:nth-child(12)").addClass("olli12");
    $("ol li:nth-child(13)").addClass("olli13");
    $("ol li:nth-child(14)").addClass("olli14");
    $("ol li:nth-child(15)").addClass("olli15");
    $("ol li:nth-child(16)").addClass("olli16");
    $("ol li:nth-child(17)").addClass("olli17");
    $("ol li:nth-child(18)").addClass("olli18");
    $("ol li:nth-child(19)").addClass("olli19");
    $("ol li:nth-child(20)").addClass("olli20"); 
</script>

change this to

    <script type="text/javascript">
        jQuery(document).ready(function ($) {
        $("ol li:nth-child(1)").addClass('olli1');
        $("ol li:nth-child(2)").addClass("olli2");
        $("ol li:nth-child(3)").addClass("olli3");
        $("ol li:nth-child(4)").addClass("olli4");
        $("ol li:nth-child(5)").addClass("olli5");
        $("ol li:nth-child(6)").addClass("olli6");
        $("ol li:nth-child(7)").addClass("olli7");
        $("ol li:nth-child(8)").addClass("olli8");
        $("ol li:nth-child(9)").addClass("olli9");
        $("ol li:nth-child(10)").addClass("olli10");
        $("ol li:nth-child(11)").addClass("olli11");
        $("ol li:nth-child(12)").addClass("olli12");
        $("ol li:nth-child(13)").addClass("olli13");
        $("ol li:nth-child(14)").addClass("olli14");
        $("ol li:nth-child(15)").addClass("olli15");
        $("ol li:nth-child(16)").addClass("olli16");
        $("ol li:nth-child(17)").addClass("olli17");
        $("ol li:nth-child(18)").addClass("olli18");
        $("ol li:nth-child(19)").addClass("olli19");
        $("ol li:nth-child(20)").addClass("olli20"); 
     });
    </script>

In my case I was using jquery on my typescript file:

import * as $ from "jquery";

But this line gives me back an Object $ and it does not allow to use as a function (I can not use $('my-selector')). It solves my problem this lines, I hope it could help anyone else:

import * as JQuery from "jquery";
const $ = JQuery.default;

There are quite lots of answer based on situation.

1) Try to replace '$' with "jQuery"

2) Check that code you are executed are always below the main jquery script.

<script src="http://code.jquery.com/jquery-1.11.3.min.js"></script>
<script type="text/javascript">
jQuery(document).ready(function(){

});
</script>

3) Pass $ into the function and add "jQuery" as a main function like below.

<script type="text/javascript">
jQuery(document).ready(function($){

});
</script>