array reduce array of objects code example

Example 1: javascript reduce array of objects

var objs = [
  {name: "Peter", age: 35},
  {name: "John", age: 27},
  {name: "Jake", age: 28}
];

objs.reduce(function(accumulator, currentValue) {
  return accumulator + currentValue.age;
}, 0); // 35 + 27 + 28 = 90

Example 2: creating array of objects usinng reduce js

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 3: reduce object to array javascript

var arr = [{x:1},{x:2},{x:4}];

arr.reduce(function (a, b) {
  return {x: a.x + b.x}; // returns object with property x
})

// ES6
arr.reduce((a, b) => ({x: a.x + b.x}));

// -> {x: 7}

Example 4: reduce javascript

/* this is our initial value i.e. the starting point*/
const initialValue = 0;

/* numbers array */
const numbers = [5, 10, 15];

/* reducer method that takes in the accumulator and next item */
const reducer = (accumulator, item) => {
  return accumulator + item;
};

/* we give the reduce method our reducer function
  and our initial value */
const total = numbers.reduce(reducer, initialValue)

Example 5: array reduce

arr.reduce(callback( accumulator, currentValue[, index[, array]] ) {
  // return result from executing something for accumulator or currentValue
}[, initialValue]);