IDBKeyRange.only creating null cursor

Question

so I am learning IndexedDB because I have to use it in a app my company is planing, and I am finding myself a bit frustrated with cursors and IDBKeyRange. The thing, everything works great until I try to 'filter' with IDBKeyRange.only. I have a 'database' with three students, two of them have the 'Sciences' course as part of their data. I have an index working towards that field (course) and when I create a cursor to iterate over the students, it works well UNTIL I try to filter. What am I doing wrong with IDBKeyRange? This is my code. Note that I placed comments to help understanding the data, etc. Thank you in advanced:

/* 
    DATA AS A REFERNCE TO UNDERSTAND
        store.put({ id: 1, name: "John Smith", gender: "Male", age: 21, course: "Sciences" });
        store.put({ id: 2, name: "Theresa Martin", gender: "Female", age: 20, course: "Arts" });
        store.put({ id: 3, name: "David Brown", gender: "Male", age: 20, course: "Sciences" });
    */

    // this index exists
    const courseIndex = store.index('course_index');

    // Am I doing something wrong with this one?
    const range = IDBKeyRange.only('Sciences');

    // If I dont pass 'range', it works well
    const courseIndexCursor = courseIndex.openCursor( range );

    courseIndexCursor.onsuccess = event => {
        const cursor = event.target.result; // this gets null if 'range' is used

        if( cursor != null ){
            console.log( cursor.value );
            cursor.continue();
        }
    }

Thank you again!

Answer 1

I was able to find the problem, at least with this one! It turns out that, when I created my course_index (during onupgradeneeded), I did it like this:

store.createIndex("course_index", ["course"], { unique: false });

So I only had to change this:

const range = IDBKeyRange.only('Sciences');

to this (I added the square brackets to the value):

const range = IDBKeyRange.only(['Sciences']);

And the code posted in my question worked perfectly. In case anyone has the same problem someday. I really thing I am missing some concepts yet, but at least it is working now.