How to decipher mapping function to key value pairs

Question

Good morning. I'm trying to decipher what this function is doing as I'm new to JS and breaking it down line by line. I also tried putting the function into Babel to see if it would be more explicit.

const t = objArray =>     
  Object.assign(
    {},
    ...objArray.map(
      ({ v, k }) => ({ [k]: v     
    }))
  );

This is what I believe is occurring:

const t = objArray =>     
  Object.assign(
    {},

an array object is being cloned with all properties of objArray

...objArray.map(
      ({ v, k }) => ({ [k]: v     
    }))
  );

This is where I get a little confused. Is objArray being mapped to a new array object where each array element holds a key and val?

Any help and tips to decipher these complex functions are greatly appreciated. Thank you

`[ { "k": "key1", "v": "value1" }, { "k": "key2", "v": "value2" } ]` -> `{ "key1": "value1", "key2": "value2" }` — Andreas, Nov 04 '19 at 15:07
`({ v, k })` -> [Destructuring assignment](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Destructuring_assignment), `...objArray` -> [Spread syntax](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Spread_syntax), `{ [k]: ... }` -> [Object initializer -> Computed property names](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Object_initializer#Computed_property_names) — Andreas, Nov 04 '19 at 15:12
[How do I convert array of Objects into one Object in JavaScript?](https://stackoverflow.com/questions/19874555/how-do-i-convert-array-of-objects-into-one-object-in-javascript) — Andreas, Nov 04 '19 at 15:21

score 1 · Accepted Answer · answered Nov 04 '19 at 15:25

This function takes an array of objects and turns it into a dictionary.

The array of objects have this shape:

[
  {
    v, // 'v' holds some value
    k // 'k' holds some value
  },
...
]

For each object in the array the function takes the value k and tunrs it into a key. The value v becomes the associated value.

If the k and v are numbered, here is what you obtain in the dictionary:

{
  [k1]: v1,
  [k2]: v2,
  [k3]: v3,
  ...
}

How to decipher mapping function to key value pairs

1 Answers1