關於幾道題

extensions is an Array and each item has such format:
{firstName: 'xxx', lastName: 'xxx', ext: 'xxx', extType: 'xxx'}
lastName, ext can be empty, extType can only has "DigitalUser", "VirtualUser","FaxUser","Dept","AO".

Question 1: sort extensions by "firstName" + "lastName" + "ext" ASC
Question 2: sort extensions by extType follow these orders ASC
DigitalUser < VitrualUser < FaxUser < AO < Dept.

/*
* 數據集合
* 基礎數據保存 + 基本數據排序操做
*/
class ExtensionsSort {
    constructor (data = []) {
        this.data = data;
        this.extTypeList = ['DigitalUser', 'VirtualUser','FaxUser', 'AO', 'Dept'];
    }

    // 校驗extType
    checkExtType (item) {
        if (this.extTypeList.indexOf(item) === -1) {
            console.log('extType can only has "DigitalUser", "VirtualUser","FaxUser","Dept","AO"');
            return false;
        }
        return true;
    }

    compareExtType (type1, type2, isAsc) {
        // extTypeList index越大優先級越高
        let idx1 = this.extTypeList.indexOf(type1);
        let idx2 = this.extTypeList.indexOf(type2);

        if (idx1 === -1 || idx2 === -1) {
            console.log('extType can only has "DigitalUser", "VirtualUser","FaxUser","Dept","AO"');
        }

        return this.compare(idx1, idx2, isAsc);
    }

   // 多屬性比較
    compareAttrs (el1, el2, attrs) {
        // attrs: [{key: 'attr1', isAsc: false}]
        let res = [];
        let len = attrs.length;
        for (let i = 0; i < len; i++) {
            let val = this.compare(el1[attrs[i].key], el2[attrs[i].key], attrs[i].isAsc);
            res.push(val);
            if (val === 1 || val === -1) break;
        }
        
        for (let j = 0; j < res.length; j++) {
            if (res[j] === 1 || res[j] === -1) return res[j];
        }

        return 0;
    }

    compare (item1, item2, isAsc) {
        if (item1 > item2) {
            return (isAsc ? 1 : -1);
        } else if (item1 < item2) {
            return (isAsc ? -1 : 1);
        } else {
            return 0;
        }
    }

}


function sortExtensionsByName(extensions) {
    let es = new ExtensionsSort(extensions);
    let attrs = [
        {
            key: 'firstName',
            isAsc: true
        },
        {
            key: 'lastName',
            isAsc: true
        },
        {
            key: 'ext',
            isAsc: true
        }
    ]

    extensions.sort((a, b) => {
        return es.compareAttrs(a, b, attrs);
    });

    return extensions;
}

function sortExtensionsByExtType(extensions, isAsc = true) {
    let es = new ExtensionsSort(extensions);
    extensions.sort((a, b) => {
        return es.compareExtType(a, b, isAsc);
    });

    return extensions;
}

saleItems is an Array has each item has such format:
{ month: n,//[1-12], date: n, //[1-31], transationId: "xxx", salePrice: number}

Question 3: write a function to calculate and return a list of total sales (sum) for each quarter, expected result like:
[{quarter: 1, totalPrices: xxx, transactionNums: n},{....}]

Question 4: write a function to calculate and return a list of average sales for each quarter, expected result like:
[{quarter: 1, averagePrices: xxx, transactionNums: n},{....}]

class QuarterData {
    constructor(saleItems = [], digits = 2){  
        // 原始數據
        this.saleItems = saleItems;

        // 季度相關數據
        this.sumOfQuarterItems = [];

        //金額保留的小數位數
        this.digits = Math.pow(10, digits);

        this.quarterData();

        return this;
    }  

    quarterData () {
        let res = [];
        this.saleItems.forEach((item) => {
            let quarterId = this.getQuarter(item.month).quarter;

            if (!res[quarterId]) {
                res[quarterId] = {
                    quarter: quarterId,
                    totalPrices: 0,
                    transactionNums: 0
                };
            } 

            res[quarterId].totalPrices = (res[quarterId].totalPrices*this.digits + item.salePrice*this.digits)/this.digits;
            res[quarterId].transactionNums += 1;
        });

        this.sumOfQuarterItems = res.filter((item) => {
            // 增長平均值
            item ? (item.averagePrices = (item.totalPrices*this.digits / item.transactionNums) / this.digits) : '';
            return item !== undefined;
        });

        return this;
    }

    // quarter
    getQuarter (month) {
        let spring = 0; //春  
        let summer = 3; //夏  
        let fall = 6;   //秋  
        let winter = 9; //冬  

        if (month < summer) {
            return {
                key: 'spring',
                quarter: 1
            };
        }

        if (month < fall) {
            return {
                key: 'summer',
                quarter: 2
            };
        }


        if (month < winter) {
            return {
                key: 'fall',
                quarter: 3
            };
        }


        return {
                key: 'winter',
                quarter: 3
            };
    }
}


function sumByQuarter(saleItems) {
    let sum = new QuarterData(saleItems).sumOfQuarterItems;
    let res = [];

    sum.forEach((item) => {
        res.push({
            quarter: item.quarter,
            totalPrices: item.totalPrices,
            transactionNums: item.transactionNums
        });
    });
    return res;
}

function averageByQuarter(saleItems) {
    let average = new QuarterData(saleItems).sumOfQuarterItems;
    let res = [];

    average.forEach((item) => {
        res.push({
            quarter: item.quarter,
            averagePrices: item.averagePrices,
            transactionNums: item.transactionNums
        });
    });

    return res;
}

Question 5: please create a tool to generate Sequence Expected to be used like:
var sequence1 = new Sequence();
sequence1.next() --> return 1;
sequence1.next() --> return 2;

in another module:
var sequence2 = new Sequence();
sequence2.next() --> 3;
sequence2.next() --> 4;

let SequenceConfig = {
    idx: 0
};

class Sequence{  
    // 構造
    constructor(incr = 1){  
        // 自增加度
        this.incr = incr;
        this.config = SequenceConfig;
    }  

    incrIdx () {
        this.config['idx'] += this.incr;
        return this.config['idx'];
    }

    next () {
        let idx = this.increaseIdx();
        return idx;
    } 
}

Question 6:

AllKeys: 0-9;
usedKeys: an array to store all used keys like [2,3,4];
We want to get an array which contains all the unused keys,in this example it would be: [0,1,5,6,7,8,9]

代碼的健壯性，很大一部分工做在入口的嚴格把控【入參的處理】
這裏會有一個通用的工具方法集合

let _utils = {
    isNumber (data) {
        return Object.prototype.toString.call(data) === '[object Number]';
    },
    isArray (data) {
        return Object.prototype.toString.call(data) === '[object Array]';
    },

    createArray (number = 9) {
        let arr = [];
        for (let i = 0; i <= number; i++) {
            arr.push(i);
        }
        return arr;
    }
};



function getUnUsedKeys (allKeys = 9, usedKeys = []) {
    _utils.isNumber(allKeys) ? allKeys = _utils.createArray(allKeys) : '';

    if (_utils.isArray(allKeys)) {
        return allKeys.filter((item) => {
            return usedKeys.indexOf(item) === -1;
        });
    } else {
        console.log('allKeys should be an array or number');
    }
}