Code:

/**
 * @param {string} s
 * @param {string} t
 * @return {boolean}
 */
var isSubsequence = function(s, t) { 
    let j = 0

    for (let i = 0; i < t.length; i++) {
        if (s[j] === t[i]) {
            j++
        }
    }

    return j === s.length
};


console.log(isSubsequence('abc', 'ahbgdc'))
console.log(isSubsequence('axc', 'ahbgdc'))