How can I use the reduce function with objects in JavaScript?

How can I use the reduce function with objects in JavaScript?

You can use the reduce function to transform an array of objects into a single object. For example, if you have an array of user objects and you want to create a single object that counts the number of users by their role, you can do it like this.

Can you show me a code example?

Sure! Here's a simple example:

const users = [
  { name: 'Alice', role: 'admin' },
  { name: 'Bob', role: 'user' },
  { name: 'Charlie', role: 'admin' }
];

const roleCount = users.reduce((acc, user) => {
  acc[user.role] = (acc[user.role] || 0) + 1;
  return acc;
}, {});

console.log(roleCount); // { admin: 2, user: 1 }

What if I want to combine properties from the objects?

You can modify the accumulator to combine properties. For instance, if you want to create an object that lists users by their roles, you can do it like this:

const groupedByRole = users.reduce((acc, user) => {
  if (!acc[user.role]) {
    acc[user.role] = [];
  }
  acc[user.role].push(user.name);
  return acc;
}, {});

console.log(groupedByRole); // { admin: ['Alice', 'Charlie'], user: ['Bob'] }