JavaScript遍历数组，将price属性乘以2

Question

I'm trying to loop through amusementRides in the doublePrices function below, multiplying the price by 2 but I get nothing in return. What am I missing?

var amusementRides = [  
   {  
      id:'A1',
      name:'superman',
      price:12,
      opening_dates:[  
         'Monday',
         'Tuesday',
         'Wednesday',
         'Thursday',
         'Friday',
         'Saturday',
         'Sunday'
      ],
      children_access:false
   },
   {  
      id:'A2',
      name:'raging bull',
      price:10,
      opening_dates:[  
         'Saturday',
         'Sunday'
      ],
      children_access:false
   },
   {  
      id:'A3',
      name:'teacups',
      price:7,
      opening_dates:[  
         'Friday',
         'Saturday',
         'Sunday'
      ],
      children_access:true
   }
];

// Define variable
var amusementRidesDouble = doublePrices(amusementRides);

// Define function to multiply price by 2
function doublePrices(amusementRides) {

    for (var price in amusementRides) {
        if amusementRides.hasOwnProperty(price) {
            alert (price *= 2);
    }
}
}

console.log(amusementRidesDouble);

Thanks in advance!

Answer 1

You can use map function of array and update required fields

function doublePrices(amusementRides) {
    amusementRidesdouble = amusementRides.map(function(item){
        item.price = 2 * item.price;
        return item;
   })
   return amusementRidesdouble;

}

Answer 2

amusementRides is an array, it is not defined as key values

change the method to

for (var counter = 0; counter < amusementRides.length; counter++) 
  {
     if (amusementRides[counter].price) 
       {
            alert (amusementRides[counter].price * 2);
            amusementRides[counter].price *= 2;
        }
  }

Answer 3

A good approach would be:

var doublePrices = function( data ) {
    data.forEach( function( item ) {
        item.price *= 2;
    }
    return data;
}

Answer 4

you should avoid for-in loop with array

you can use forEach:

amusementRides.forEach(function(item) {
  item.price *= 2;
});

Answer 5

for (var i=0; i<amusementRides.length; i++) { 
amusementRides[i].price*=2;
}

Answer 6

I think the only mistake in your code is you have tried to foreach loop like in C#. In Javascript you can't do that way.

You can modify your code like below.

for ( var i=0;i<amusementRides.length;i++) {
    var price=amusementRides[i];
        alert (price *= 2);
}

But the best approach will be :

amusementRides = amusementRides.forEach( function( item ) {
                 item.price *= 2;
              }