lib/common-part.js
function findLastCommonIndex(xs, ys) {
    for (let i = Math.min(xs.length, ys.length) - 1; i >= 0; --i) {
        if (xs[i] === ys[i]) {
            return i
        }
    }
    return -1
}
function findLastCommonIndex(xs, ys) {
    for (let i = Math.min(xs.length, ys.length) - 1; i >= 0; --i) {
        if (xs[i] === ys[i]) {
            return i
        }
    }
    return -1
}
function findLastCommonIndex ( xs , ys ) { for ( let i = Math . min ( xs . length , ys . length ) - 1 ; i >= 0 ; -- i ) { if ( xs [ i ] === ys [ i ] ) { return i } } return - 1 }
Get the index of the last element which is same between the given 2 elements.

@param {string[]} xs - An array to compare.
@param {string[]} ys - Another array to compare.
@returns {number} The index of the last element is same.
@private
Get the index of the last element which is same between the given 2 elements .