Write a program to merge strings alternately

The problem:

You are given two strings word1 and word2. Merge the strings by adding letters in alternating order, starting with word1. If a string is longer than the other, append the additional letters onto the end of the merged string.

Return the merged string.

Example #1:

Input: word1 = "abc", word2 = "pqr"
Output: "apbqcr"
Explanation: The merged string will be merged as so:
word1:  a   b   c
word2:    p   q   r
merged: a p b q c r

Example #2:

Input: word1 = "ab", word2 = "pqrs"
Output: "apbqrs"
Explanation: Notice that as word2 is longer, "rs" is appended to the end.
word1:  a   b 
word2:    p   q   r   s
merged: a p b q   r   s

Example #2:

Input: word1 = "abcd", word2 = "pq"
Output: "apbqcd"
Explanation: Notice that as word1 is longer, "cd" is appended to the end.
word1:  a   b   c   d
word2:    p   q 
merged: a p b q c   d

The solution:

    const mergeAlternately = (word1, word2) => {
        const word1Length = word1.length;
        const word2Length = word2.length;
        let i = 0, j = 0, output = '';

        while (i < word1Length || j < word2Length) {
            if (i < word1Length) {
                output +=word1[i++];
            }
            
            if (j < word2Length){
                output +=word2[j++];
            }
        }
        return output;
    };
    const word1 = 'abc';
    const word2 = 'pqr';
    console.log(mergeAlternately(word1, word2)); // apbqcr