Get index of Object inside Array and use it in a function

Question

In Javascript, is it possible to get the Index of the object (in an array of objects) and use it inside of the same object in a function?

For example:

const foo = [
 {
 id: 1,
 comments: getComments(this.index) // index of the object goes here
 },
 {
 id: 34,
 comments: getComments(this.index) // index of the object goes here
 },
 {
 id: 21,
 comments: getComments(this.index) // index of the object goes here
 }
]
const getComments = function(index) {
 return foo[index].id // return the ID of the actual object
}

Or is there a workaround for what I'm trying to achieve here?

• Barmar: At the time you're calling the function, the array doesn't even exist yet.
• evolutionxbox: What is this.index supposed to be?
• Barmar: Why do you need the index instead of the object itself?
• evolutionxbox: Also getComments won't exist when the array is defined. (I am confused)
• Barmar: If this worked, you would just be setting comments to the same thing as the id property. What's the point of that?

Answer 1

Do it in two steps. First create the array of objects, then fill in the comments property by calling the function on each element.

const foo = [
 {
 id: 1,
 },
 {
 id: 34,
 },
 {
 id: 21,
 }
]
foo.forEach(el => el.comments = getComments(el));
function getComments(obj) {
 return obj.id;
}
console.log(foo);

• Radical_Activity: Really nice, it makes sense to run a function after the array has been created. How silly of me to not thinking of that. Thanks for pointing it out.

Answer 2

I assume this is for learning purposes as probably the use you are thinking could be implemented in a better way. The closest that you can do is this:

let foo = [
 {
 id: 1,
 },
 {
 id: 34,
 },
 {
 id: 21,
 }
]
foo = foo.map(
 (elem, index) => ({...elem, comments: getComments(index)})
)
function getComments(index) {
 return foo[index].id // return the ID of the actual object
}
console.log(foo[2].comments)