Check your index.html tab, you will see links there that pull in additional code from other places. Notice how there are several
<script> tags. Those tags are what you use to gain access to other scripts that are external to your code.
You should see links to three external files plus your own main.js file.
If you'd like to see what those files contain, take the URL and visit it with your browser, it will display as plain text. You might think that the alphabet.js file is a bit messy and hard to read. To see the code in an easier to read format, copy all of the code and paste it into a code beautifying tool like http://jsbeautifier.org/
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