Array Methods

Array.reduce for object

var obj = [
  {
    id: 5,
    count: 7,
  },
  {
    id: 3,
    count: 45,
  },
  {
    id: 8,
    count: 35,
  },
  {
    id: 1,
    count: 15,
  },
];

let res = obj.reduce(
  (acc, next) => {
    return {
      id: acc.id + next.id,
      count: acc.count + next.count,
    };
  },
  {
    id: 0,
    count: 0,
  },
);

console.log(res); // {count: 102,id: 17}

Array.sort for object

var obj = [
  {
    id: 5,
    count: 7,
  },
  {
    id: 3,
    count: 45,
  },
  {
    id: 8,
    count: 35,
  },
  {
    id: 1,
    count: 15,
  },
];

let sorted = obj.sort((a, b) => {
  return a.id - b.id;
});

Slice and Splice

Slice

Think of "slicing" as cutting a portion out of an array without modifying the original array. slice returns a shallow copy of a portion of an array, specified by a start and end index.

const originalArray = [1, 2, 3, 4, 5];
const newArray = originalArray.slice(1, 4); // Returns [2, 3, 4]

Splice

Think of "splicing" as modifying or changing the original array. splice is used to add or remove elements from an array at a specified index.

const originalArray = [1, 2, 3, 4, 5];
originalArray.splice(2, 1); // Removes 1 element at index 2
// originalArray is now [1, 2, 4, 5]

Remember the keyword associations: "slice" for creating a new sliced array, "splice" for modifying the original array by splicing in or out elements.

In summary:

• slice does not modify the original array and returns a new array.

• splice modifies the original array by adding or removing elements.