如果数组包含重复项，如何为数组中的每个元素赋予唯一的ID？

Question

I have an JSON file with an array of 8 objects.

I need to turn it into array with 16 objects, where each object repeats twice and give each of these objects an individual id

I managed to duble number of elements like this

let d = data.reduce(function (res, current) {
        return res.concat([current, current]);
    }, []);

Then I tried adding ids like so

d.forEach((item, index) => {
        item.id = index;
    })

And I'm not sure why but all duplicates get the same id

Structure of JSON object

[
  {
    "name": "name",
    "description": "description"
  }
]

Code

export const fetchData = () => dispatch => {

    let d = data.reduce(function (res, current) {
        return res.concat([current, current]);
    }, []);

    d.forEach((item, index) => {
        item.id = index;
    });

    dispatch({
        type: FETCH_DATA,
        payload: d
    });
  };

Answer 1

current is a reference object, you would need Object.assign({}, current) inside your array to make sure you get 2 copies of the original object, like so:

let d = data.reduce(function (res, current) {
    return res.concat([Object.assign({}, current), Object.assign({}, current)]);
}, []);

Or with the spread operator, like so

let d = data.reduce(function (res, current) {
    return res.concat([{...current}, {...current}]);
}, []);

Answer 2

As other have mentioned, the issue if you are mutating the same object reference instead of creating new ones.

You can also move the ID assignment into reduce as well:

 const data = [ { "name": "name", "description": "description" }, { "name": "name2", "description": "description2" } ] const d = data.reduce((res, current) => [ ...res, { ...current, id: res.length }, { ...current, id: res.length + 1 }], []); console.log(d);