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JavaScript JavaScript Objects Loop Through Objects Store Objects in Arrays

Posted by Embie Wong
Embie Wong
3,180 Points

I don't understand some parts

Hi, I understand how to convert multidimensional arrays to objects, but I'm a bit confused with changing the for loop. In the video, the for loop looks like this:

for (let i = 0; i < questions.length; i++) {
   let question = questions[i].question;
   let answer = question[i].answer;
}

Since the questions array was converted into an object, doesn't it now have an index length of one? If so, that means the loop will only run once. Does the questions[i].question code run all the objects in the array?

Gareth Moore
Gareth Moore
7,724 Points
Gareth Moore
Gareth Moore
7,724 Points

The questions array was not converted into an object. The questions array is still an array. The values inside the questions array are now objects. Thus, the loop operates as normal because it is still an array.

See below, pay attention to [] which indicates arrays, and {} which indicates objects.

//normal array - notice all block braces
const questions = [
   ["What are frogs?", "No idea."],
   ["Why do I have an appendix?", "Because"]
];

//normal object - notice all curly braces
const questions = {
   {question: "What are frogs?",  answer: "No idea."},
   {question: "Why do I have an appendix?",  answer: "Because"}
};

//array with objects inside - notice block braces outside and curly braces inside
const questions = [
   {question: "What are frogs?",  answer: "No idea."},
   {question: "Why do I have an appendix?",  answer: "Because"}
];

1 Answer

Jonathan Grieve
MOD
Jonathan Grieve
Treehouse Moderator 91,253 Points
Jonathan Grieve
Jonathan Grieve
Treehouse Moderator 91,253 Points

The loops doesn't change the length, (that is the number of items in the data)

To break it down, questions refers to the variable that stores the object, which is why we have length as the property in the loop expression.

for (let i = 0; i < questions.length; i++) {
}

And inside we're looping through the key-value pairs of the object where question and answer are properties of the object. 

for (let i = 0; i < questions.length; i++) {
   let question = questions[i].question;
   let answer = questions[i].answer;
}

There's no messing around with the actual values in the property. All we're doing here is iterating through them so the values can be displayed. :-)