How to use variables in dot notation in Google Cloud Firestore

Question

I want to update fields in nested objects in my Cloud Firestore by using dot notation. But those fields referenced by the dot notation are variables.

How can I do that?

Documentation

// To update age and favorite color:
db.collection("users").doc("frank").update({
    "age": 13,
    "favorites.color": "Red"
})

But what if I need to make favorites.color a variable?

const attributes = [ 'jobs', 'schools', 'favorites', ];
const values = [ 'food', 'song', 'color', ];
const variableData = [attributes[2]].[values[2]]; // 'favorites.color'

Can I do:

db.collection("users").doc("frank").update({
  "age": 13,
  "[attributes[2]].[values[2]]": "Red"
})

How, exactly, would this work?

Edit:

Failed attempts

I tried:

db.collection("users").doc("frank").update({
  "age": 13,
  `${[attributes[2]]}.${[values[2]]}`: "Red"
})

and got the following error:

Parsing error: Unexpected token

Same error also occurs when trying

`"${[attributes[2]]}.${[values[2]]}"`: "Red"

(Thinking that Firebase needs the quotation marks to parse the syntax.)

Answer 1

The key thing you are missing is that when you are using computed property names, you need to wrap the expression in []. For example, you should write it as the following:

db.collection("users").doc("frank").update({
  "age": 13,
  [`${attributes[2]}.${values[2]}`]: "Red"
})

Runnable example:

const attributes = [ 'jobs', 'schools', 'favorites', ];
const values = [ 'food', 'song', 'color', ];

console.log({
  age: 13,
  [`${attributes[2]}.${values[2]}`]: 'red'
})

NOTE: Quotes do not matter when writing out keys in javascript. We only use backticks here because we want the each of the values ("favorite", "color") to be joined together by a dot.