Filter Matching and Unspecified Values

Introduction

In this lab, we will explore JavaScript programming and learn how to use the Array.prototype.reduce(), Array.prototype.filter(), and Array.prototype.map() methods together to create a function that filters an array of objects based on a condition and also filters out unspecified keys. This lab will help improve our understanding of functional programming in JavaScript and how to manipulate arrays of objects in a concise and efficient manner.

Filtering Objects by Condition and Keys

To filter an array of objects based on a condition, while also filtering out unspecified keys, use the reducedFilter() function.

Here are the steps to follow:

1. Use Array.prototype.filter() to filter the array based on the predicate fn so that it returns the objects for which the condition returned a truthy value.

2. Use Array.prototype.map() on the filtered array to return the new object.

3. Use Array.prototype.reduce() to filter out the keys which were not supplied as the keys argument.

const reducedFilter = (data, keys, fn) =>
  data.filter(fn).map((el) =>
    keys.reduce((acc, key) => {
      acc[key] = el[key];
      return acc;
    }, {})
  );

Here is an example usage of the reducedFilter() function:

const data = [
  {
    id: 1,
    name: "john",
    age: 24
  },
  {
    id: 2,
    name: "mike",
    age: 50
  }
];

reducedFilter(data, ["id", "name"], (item) => item.age > 24);
// Output: [{ id: 2, name: 'mike'}]

To start practicing coding, open the Terminal/SSH and type node.

Summary

Congratulations! You have completed the Filter Matching and Unspecified Values lab. You can practice more labs in LabEx to improve your skills.