This inserts "Hello there" text at the cursor:

    var ed = tinymce.activeEditor;
    var text = 'Hello there';
    ed.execCommand('mceInsertContent', false, text);

This inserts "Hello there" (bolded HTML) at the cursor:

    var ed = tinymce.activeEditor;
    var html = '<p style="font-weight:bold;">Hello there</p>';
    ed.execCommand('mceInsertContent', false, html);

Hope this helps.

Strange. It should work. Try this:

setTimeout(function() {
    alert(tinymce.activeEditor);
}, 5000);

It should pop up after 5 seconds with the message "[object Object]". If it says "undefined", then you are doing something wrong either with the editor or else your Javascript isn't "reaching" the editor.

Let me know what you get and we can troubleshoot from there.

Thank you so much, my problem solved. I have another question: How ca I clear all text inside the editor?

Use the "New Document" button or this code:

    ed.execCommand('mceSetContent', false, '');

(in fact, that is the code that the "newdocument" button uses!)