reduce arrau code example

Example 1: reduce array to object javascript

const posts = [
    {id: 1, category: "frontend", title: "All About That Sass"},
    {id: 2, category: "backend", title: "Beam me up, Scotty: Apache Beam tips"},
    {id: 3, category: "frontend", title: "Sanitizing HTML: Going antibactirial on XSS attacks"}
];

const categoryPosts = posts.reduce((acc, post) => {
    let {id, category} = post;
    return {...acc, [category]: [...(acc[category] || []), id]};
}, {});

Example 2: reduce method

The reduce() method executes a reducer function (that you provide) on each element of the array, resulting in single output value.

The reducer function takes four arguments:
Accumulator (acc)
Current Value (cur)
Current Index (idx)
Source Array (src)

//syntax
arr.reduce(callback( accumulator, currentValue, [, index[, array]] )[, initialValue])
//example flatten an array

let flattened = [[0, 1], [2, 3], [4, 5]].reduce(
  ( accumulator, currentValue ) => accumulator.concat(currentValue),
  []
)