Difference in paths

diff.js

// Given two absolute paths on a file system, write a function to determine the difference between them.
// For example, `/a/b/c` and `/a/d` should yield `../../d`.

// `/a/b/c` and `/e/f` => `../../../e/f`
// `/` and `/a/b/c` => `/a/b/c`
// `/a/b/c` and `/` => `../../../`


function difference(path1, path2) {
    // break the paths into lists and discard the first empty element
    path1List = path1.split('/').slice(1);
    path2List = path2.split('/').slice(1);

    // if path1List's first element is empty, we can just cd into path2
    if( path1List[0] === '' ) {
      return path2List.join('/');
    }

    // figure out how deep both paths have in common
    // saved as depth
    let depth = 0;
    for(let i=0; i<path1List.length; i++ ) {
        if( path1List[i] != path2List[i] ) {
            depth = i;
            break;
        }
    }

    // set up returnedPath to contain the return value
    let returnedPath = "";
    // looping through the number of directories we go need to go up
    for(let j=0; j < (path1List.length - depth); j++ ) {
        returnedPath += '../'
    }

    // if path2 doesn't have anything, we can return the path so far
    if( path2List[0] === '' ) {
      return returnedPath.slice(0,returnedPath.length-1);
    }
    // descending from our common directory into path2
    for(let k=depth; k< path2List.length; k++ ) {
      returnedPath += path2List[k] + '/';
    }

    return returnedPath.slice(0,returnedPath.length-1)
}

console.log('*** TEST CASE 1 ******************');
console.log(difference(`/a/b/c`, `/a/d`)=== `../../d`);

console.log('*** TEST CASE 2 ******************');
console.log(difference(`/a/b/c`, `/e/f`) === `../../../e/f`);

console.log('*** TEST CASE 3 ******************');
console.log(difference(`/`, `/e/f`) === `e/f`);

console.log('*** TEST CASE 4 ******************');
console.log(difference(`/e/f`, `/`) === `../..`);