"el" is a parameter of the function that is used in filter, it will save the elements of the array in each iteration of filter, so he uses "el" in the function to have each character in the array. I think he named the parameter "el" because of "element". The reason it maybe look's something weird it's because he use a "function expresion"( function(){} ) instead of a "arrow function"( () => {} )

I like the approach.

My suggestion is that you breakdown the code by methods like the filter method.

Example: filter()

const words = ['spray', 'limit', 'elite', 'exuberant', 'destruction', 'present'];

const result = words.filter(word => word.length > 6);

console.log(result);
// expected output: Array ["exuberant", "destruction", "present"]

I think it's better to put the letters into an object?

Took me a second too see it. This way you don't have to run a contains on every letter. I like it

i like it

does it gonna change the output to all lowercase which is not as expected?

should rather have used... the spoiler flag...