Question 187402 in Javascript Question posted in
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Javascript – why the object of my code is outputing undefined if it has a value? I compared my code with other similar ones that work and I can't see the error

I am trying to console.log the typeOne(or any other type) property of each object in the donuts array, but I keep getting undefined as the output. My editor is showing that the problem is at the colon character in the object literals, suggesting that I should print a comma instead. However, I believe that is incorrect. What is the issue here and how can I fix it?

var donuts = [
  { typeOne: "Jelly", cost: 1.22 },
  { typeTwo: "Chocolate", cost: 2.45 },
  { typeThree: "Cider", cost: 1.59 },
  { typeFour: "Boston Cream", cost: 5.99 }
];
console.log(donuts.typeOne);
//or
console.log(donuts["typeOne"]); //both console.log shows undefined
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4

Answers


  1. 0

    In your example donuts is an array not an object (it’s an array of objects). To print the first item, you have to write donuts[0].typeOne. You are getting undefined because you are treating the donuts variable as an object instead of an array.

    Hope it helps!

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  2. 0

    Because donuts is an array. You can reference items in an array by their indexes.

    For example:

    var donuts = [
  { typeOne: "Jelly", cost: 1.22 },
  { typeTwo: "Chocolate", cost: 2.45 },
  { typeThree: "Cider", cost: 1.59 },
  { typeFour: "Boston Cream", cost: 5.99 }
];

console.log(donuts[0].typeOne);
//or
console.log(donuts[1]["typeTwo"]);

    You could make things are little more interesting if you change type<Number> to name and do something like this:

    var donuts = [
  { name: "Jelly", cost: 1.22 },
  { name: "Chocolate", cost: 2.45 },
  { name: "Cider", cost: 1.59 },
  { name: "Boston Cream", cost: 5.99 }
];
    
console.log(donuts.find(d => d.name == "Chocolate").cost);
//or
console.log(donuts.filter(d => d.cost < 2.0 ));
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  3. 0

    You are trying to access the property typeOne directly from donuts. But donuts is an array of objects, not a direct object. If you want to get the property typeOne from each object in your array, you need to go at each item with some method like map:

    var result = donuts.map((donut) => donut.typeOne)

    Problem is, the property typeOne only exists in the first object of your array, so result here will be ["Jelly", undefined, undefined, undefined]

    To list all types from each object in your array I suggest this:

    var donuts = [
  { type: "Jelly", cost: 1.22 },
  { type: "Chocolate", cost: 2.45 },
  { type: "Cider", cost: 1.59 },
  { type: "Boston Cream", cost: 5.99 }
];

var result = donuts.map((donut) => donut.type)

    In this case, type is a property in every object, so when you use map you iterate through all the objects in your array and get the value of the property type.

    Hope it helps

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  4. 0

    So your object "typeOne", is an an array.
    You have to access the object in the array, then the objects properties.

    

//you declare and object like this
var obj = {
   key: 'value'
};
console.log(obj.key);

//you declare a array like this
var array = [
    'val1',
    'val2'
];
//to access a arrays value you have to use its index
console.log(array[0])//index starts at zero in javascipt, not one

//so if you have a object in a array, like here
var donuts = [
  { typeOne: &quot;Jelly&quot;, cost: 1.22 },
  { typeTwo: &quot;Chocolate&quot;, cost: 2.45 },
  { typeThree: &quot;Cider&quot;, cost: 1.59 },
  { typeFour: &quot;Boston Cream&quot;, cost: 5.99 
]
//you first have to, you first have to get the object using by its index
console.log(donuts[0])//the arrays firsts value: {typeOne etc)

//so now to access the arrays object properties, just get the object from the array first like above, then the properties
console.log(donuts[0].typeOne)

//or you can get the second object
console.log(donuts[1].typeTwo)
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