javascript- How to check if an object as a specific property

Question

I have this code, used to get a number of hours from an object and multiply them by a variable.

Here is the object 'work'

var work = [
    {'day': 27, 'hours': 7.30},
    {'day': 29, 'hours': 7.30},
    {'day': 31, 'hours': 10},
    {'day': 1, 'hours': 8.30},
    {'day': 2, 'hours': 7},
    {'day': 3, 'hours': 7},
    {'day': 5, 'hours': 7.30},
    {'day': 6, 'hours': 7},
    {'day': 7, 'hours': 7.30},
    {'day': 8, 'hours': 8},
    {'day': 9, 'hours': 9.30}
]

var payPerHour = 7;

and here my function to calculate the pay

function calculatePay()
{
    var result = 0, fResult = 0;

    for(var i = 0; i < work.length; i++) {
        Object.keys(work).forEach(function (val) {
            if (work[i].hasOwnProperty('hours'))
              result = work[i][val] * payPerHour;

            fResult += result;
        });
    }

    return fResult;
} 

I have used "hasOwnProperty" to check if the property "hours" exists in work. The result of the function is NaN. Why?

Answer 1

You're already iterating your array via the for loop - then you do

Object.keys(work).forEach(function(val) {

This doesn't make any sense. work is an array - not an object. Basically if you remove that line it'll work:

for(var i = 0; i < work.length; i++) {
  //Object.keys(work).forEach(function(val) {
    if(work[i].hasOwnProperty('hours'))
      result = work[i]["hours"] * payPerHour; //use the right property here

    fResult += result;
  //});
}

A simpler way may be to use Array.reduce

var totalHourPay = work.reduce(function(total, workDay) {
    if (workDay.hasOwnProperty("hours")) {
         total += workDay.hours * payPerHour;
    }

    return total;
}, 0);

Answer 2

You can use Javascript for..in loops like below:

 function calculatePay() { var result = 0, fResult = 0; for(var index in work) { if(work[index].hasOwnProperty('hours')) result = work[index]['hours'] * payPerHour; fResult += result; } return fResult; } 

Answer 3

Why these complicated expressions? Try this ES6 solution:

 var work = [{'day':27,'hours':7.30},{'day':29,'hours':7.30},{'day':31,'hours':10}, {'day':1,'hours':8.30},{'day':2,'hours':7},{'day':3,'hours':7}, {'day':5,'hours':7.30},{'day':6,'hours':7},{'day':7,'hours':7.30}, {'day':8,'hours':8},{'day': 9, 'hours': 9.30}], calculatePay=(b)=>work.reduce((c,d)=>c+d.hours*b,0) // Test console.log( calculatePay(7) ) // Returns 600.6 and 7 is your rate per hour // Or redefine function calculatePay this way if you need ES5 compatibility // function calculatePay(a) { // return work.reduce(function(b,c) { // return b + c.hours * a // }, 0) // } // And if you really needs use hasOwnProperty, define it this way // function calculatePay(a) { // return work.reduce(function(b,c) { // return b + (c.hasOwnProperty('hours') && c.hours || 0) * a // }, 0) // } // But you dont need hasOwnProperty. You are processing simple array, // not object. And this array is full of ordinary object literals. None of // them does not inherits anything from another object, unless you override // Object itself. 

Answer 4

I believe this is what you wanted:

var work = [{'day': 27, 'hours': 7.30},
      {'day': 29, 'hours': 7.30},
      {'day': 31, 'hours': 10},
      {'day': 1, 'hours': 8.30},
      {'day': 2, 'hours': 7},
      {'day': 3, 'hours': 7},
      {'day': 5, 'hours': 7.30},
      {'day': 6, 'hours': 7},
      {'day': 7, 'hours': 7.30},
      {'day': 8, 'hours': 8},
      {'day': 9, 'hours': 9.30}
      ];

var payPerHour = 7;

var result = 0, fResult = 0;

function calculatePay(){

for(var i = 0; i < work.length; i++) {
   Object.keys(work).forEach(function() {

   result = work[i].hours * payPerHour;
   fResult += result;
 });

}

console.log("Final total: " +fResult);
}

calculatePay();