isSubsequence.js

/**
 * @param {string} s
 * @param {string} t
 * @return {boolean}
 */
var isSubsequence = function(s, t) {
    var indexCount = 0;
    
    if (s === "") {
        return true;
    }
    
    for (var i = 0; i < t.length; i++) {
        if (t[i] === s[indexCount]) {
            if (indexCount === s.length - 1) {
                return true;
            }
            indexCount++;
        }
    }
    
    return false;
};