javascript 中的函数（部分函数）

Question

编写一个名为 displayDayNumber(dateString) 的函数（不是生成器），它满足以下规则。

var dayNumber =displayDayNumber("Nov 5,2017");  //309
console.log(dayNumber ()); // 310
dayNumber("Oct 31 2017"));  //304
dayNumber();//305

到目前为止，我的代码可以处理一次 dateString 传递值，但它不是基于我在 dayNumber 中传递新值时计算的。

var dayNumber =function(dateString=new Date().toDateString())
{
var currentString=dateString;
var no=dateString.substring(8,10);
// console.log(no);

    return function () {
       // console.log("dateString=",dateString);
        var b = calculateNumber(dateString)   //helper function to calculate day No
        {

            var no = dateString.substring(8, 10);
            var toNo = parseInt(no) + 1;
            var thenString = toNo.toString() + ' ';
            var replacecharacter = dateString.replace(no, thenString);
            dateString = replacecharacter;
            return b;
        };
        return dateString;
    };

}

let genDayNumber=dayNumber ("Sat Nov 05 2017"); //309  //working 
genDayNumber();     //working
genDayNumber("Wed Oct 31 2017")); //304   not working
genDayNumber();     //not working

Answer 1

const dayNumber = date => {
  let days = new Date(date).getDay();
  return arg => {
    if(arg){
       return days = new Date(arg).getDay();
    }
    return ++days;
  };
};

Answer 2

您返回的函数不带参数，因此当您传入 "Wed Oct 31 2017" 时，它会被忽略。

您需要修改返回的函数以接受一个值。

这是一个工作示例

var dayNumber =displayDayNumber("Nov 5,2017");  //309
console.log(dayNumber); // 309
console.log(dayNumber()); // 310

console.log(dayNumber("Oct 31 2017"));  //304
console.log(dayNumber())//305


function displayDayNumber(str) {
    let date = new Date(str);
    let day = dayOfYear(date);

    var result = function(str) {
        if (str) {
            day = displayDayNumber(str);
            return day;
        } else {
            return ++day;
        }
    }

    result.valueOf = result.toString = function() { return day; }
    return result;
}

function dayOfYear(now) {
    // Taken from 
    var start = new Date(now.getFullYear(), 0, 0);
    var diff = (now - start) + ((start.getTimezoneOffset() - now.getTimezoneOffset()) * 60 * 1000); 
    var oneDay = 1000 * 60 * 60 * 24;
    var day = Math.floor(diff / oneDay);
    return day;
}

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