codemirror how to install

Question 1

does this points you to the right direction?

        <link rel="stylesheet" href="lib/codemirror.css">
        <script src="lib/codemirror.js"></script>
        <script src="mode/javascript/javascript.js"></script>
        <script src="addon/fold/foldcode.js"></script>
    </head>
    <body>
        <form style="width:500px;">
            <textarea id="code" name="code">
alert("HI");
//says HII
            </textarea>
        </form>

        <script>
            window.onload = function() {
                window.editor = CodeMirror.fromTextArea(code, {
                    mode: "javascript",
                    lineNumbers: true,
                    lineWrapping: true,
                    foldGutter: {
                        rangeFinder: new CodeMirror.fold.combine(CodeMirror.fold.brace, CodeMirror.fold.comment)
                    },
                    gutters: ["CodeMirror-linenumbers", "CodeMirror-foldgutter"]
                });
            };
        </script>
    </body>
</html>

Question 2

First: you have to select the first element that matches the selector.

$("#editor") won't do it, it has to be $("#editor")[0]

Second: The following code is all you need to get it to work:

window.onload = function () {
    var editor = CodeMirror.fromTextArea($("#editor")[0], {
        lineNumbers: true,
        lineWrapping: true,
    });
};

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<html>    
    <head>
        <script src="https://cdnjs.cloudflare.com/ajax/libs/codemirror/5.29.0/codemirror.js"></script>
        <link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/codemirror/5.29.0/codemirror.css">
        <script src="https://cdnjs.cloudflare.com/ajax/libs/codemirror/5.29.0/mode/javascript/javascript.js"></script>
    </head>
    <body>
        <p>Type some javascript below</p>
        <textarea id="editor"></textarea>
    </body>
</html>