Difference between compareLetters() and isSubsequence() helper function?

Hi all. I completed the ‘Letter Lookup’ and ‘Subsequence’ course in Intro to Interviewing, and I was wondering where is the different between compareLetters() and isSubsequence() helper function. For example with compareLetters() helper function:

let word = 'apple';
let mappedObject = {
    a: [0], // a
    b: [1], // b
    p: [2, 3, 4], // ppp
    l: [5], // l
    e: [6, 7] // ee
};
// mappedObject is now abppplee.
compareLetters(word, mappedObject); /* This function right there! */

And the isSubsequence() helper function:

let word = 'apple';
let mappedObject = {
    a: [0], // a
    b: [1], // b
    p: [2, 3, 4], // ppp
    l: [5], // l
    e: [6, 7] // ee
};
// mappedObject is now abppplee.
isSubsequence(word, mappedObject); /* This function right there! */

Please answer as fast as possible. :blush:

Thank you!
Pummarin :smile: