SOURCE

var letterCombinations = function(digits) {
    let zimuObj = {
        d2: ['a','b','c'],
        d3: ['d','e','f'],
        d4: ['g','h','i'],
        d5: ['j','k','l'],
        d6: ['m','n','o'],
        d7: ['p','q','r','s'],
        d8: ['t','u','v'],
        d9: ['w','x','y','z'],
    }

    let zimuArr = []
    let len = digits.length
    for(let i = 0; i<len; i++){
        zimuArr.push(zimuObj[`d${digits[i]}`])
    }
    console.log(zimuArr)
};

console.log(letterCombinations("23"))