How to write using typescript a function able to add or replace an element from an array of Objects

user_16926559 0
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I want to create a function that takes in input an array of Objects, an Object, and a key and returns an Array of Objects that contains the new Object on position 0 if it's a new Object or at the same position if it's not a new one. The key is used to compare the Objects and can be only a string or a number.

I wrote this one but it's mandatory to have an id property inside the Objects.

export function addOrReplaceById<T extends Array<{ id: string }>>(
  arrayOfObjects: T,
  newObject: { id: string }
): T {
  const index = arrayOfObjects.findIndex((object) => object.id === newObject.id);

  if (index === -1) {
    arrayOfObjects.unshift(newObject);
  } else {
    arrayOfObjects[index] = newObject;
  }
  return arrayOfObjects;
}
typescript object arrays javascript
2 Answers

Consider this example:

export function addOrReplaceById<
    Obj extends { id: string },
    Arr extends Array<Obj>
>(
    arrayOfObjects: [...Arr],
    newObject: Obj
) {
    const data = arrayOfObjects
        .reduce<{ exists: boolean, arr: Obj[] }>(
            (acc, obj) =>
                obj.id === newObject.id ? {
                    ...acc,
                    exists: true,
                    arr: [...acc.arr, newObject]
                } : acc, {
            exists: false,
            arr: []
        });

    return data.exists ? data.arr : [newObject, ...data.arr]
}

Above example will reduce a complexity a bit. unshift operation is expensive. That's why I created new data structure {exists: boolean, arr:Obj[]}.

Also I have returned new array instead of mutation of existing array

user_84952540

You can write your function like this:

export function addOrReplaceByKey<T extends {[x: string]: any}>(
    arrayOfObjects: T[],
    newObject: T,
    key: keyof T,
): T[] {
    const index = arrayOfObjects.findIndex((object) => object[key] === newObject[key]);

    if (index === -1) {
        arrayOfObjects.unshift(newObject);
    } else {
        arrayOfObjects[index] = newObject;
    }
    return arrayOfObjects;
};
user_58461910
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