isSubsequence = function(s, t) {
    
    if(!s.length || (s === t)) return true;
    if(s.length > t.length) return false;
    
    let j = 0;
    
    for(let i = 0; i < t.length && j < s.length; i++) {
        if(s[j] === t[i]) {
            j++;
        }
    }
    
    return j === s.length;
}
Time O(N) | Space O(1)
@param {string} s
@param {string} t
@return {boolean}