You can write your JS code without any alphabet character, seriously! I would say even more you can write your JS code only with 6! characters: []()!+

You could easily get several string like “true”, “false”, “undefined” and other by doing simple operations with brackets:

and now you can take any letter :

You can try to challenge yourself and convert any JS code into this format (that is called JSFuck) and there is even online converter that will help you with this task.