https://leetcode.com/problems/is-subsequence/

isSubsequence.js

/**
 * @param {string} s
 * @param {string} t
 * @return {boolean}
 */
var isSubsequence = function(s, t) {
    
    if(!s.length) return true;
    
    let i = 0;
    
    for(let j=0; j<t.length; j++){
        if(t[j] !== s[i]) continue;
        if(++i === s.length) return true;
    }
    return false;
};