Node.js Secret Weapon: You Haven't Tried in Node.js

Node.js Secret Weapon: You Haven't Tried in Node.js

Jul 2, 2023ยท

5 min read

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Lodash is a popular JavaScript library that provides utility functions for common programming tasks. One powerful feature that is often overlooked by developers is the ability to chain operations and perform lazy evaluations, which can lead to more efficient and readable code.

What is Chaining?

In Lodash, chaining allows you to perform multiple operations on a collection in a single, fluent expression. Instead of writing multiple statements or using nested function calls, you can chain multiple methods together to create a single pipeline of operations.

Here's a simple example to illustrate the concept of chaining:

const _ = require('lodash');

let numbers = [1, 2, 3, 4, 5];

// Without chaining
let doubled =, num => num * 2);
let evenNumbers = _.filter(doubled, num => num % 2 === 0);
let sum = _.reduce(evenNumbers, (acc, num) => acc + num, 0);
console.log(sum); // Output: 24

// With chaining
let result = _(numbers)
  .map(num => num * 2)
  .filter(num => num % 2 === 0)
  .reduce((acc, num) => acc + num, 0)
console.log(result); // Output: 24

As you can see, chaining makes the code more readable and expressive by creating a clear sequence of operations.

What is Lazy Evaluation?

Lazy evaluation is an evaluation strategy that delays the computation of a value until it is needed. In the context of Lodash, lazy evaluation can lead to significant performance improvements by only executing the necessary operations in a chain.

By default, Lodash chains use lazy evaluation. When you chain multiple methods together, Lodash creates a lazy wrapper object that encapsulates the sequence of operations. Instead of executing the operations immediately, Lodash waits until you invoke the value() method on the lazy wrapper. At that point, it evaluates the operations in the most efficient way possible.

Here's an example to demonstrate the benefits of lazy evaluation:

const _ = require('lodash');

let largeArray = _.range(1, 100001); // Array of 100,000 elements

// Eager evaluation (without chaining)
let squared =, num => num * num);
let evenSquares = _.filter(squared, num => num % 2 === 0);
let firstTenEvenSquares = _.take(evenSquares, 10);

// Lazy evaluation (with chaining)
let result = _(largeArray)
  .map(num => num * num)
  .filter(num => num % 2 === 0)

In this example, the eager evaluation approach computes the square of every element in the array and filters all even squares before taking the first ten. In contrast, the lazy evaluation approach only computes the squares and filters the even ones until it has found the first ten. This results in fewer computations and better performance.

Combining Chaining and Lazy Evaluation

By combining chaining and lazy evaluation, you can write more efficient and readable code in Lodash. Here's a more complex example that demonstrates the benefits of this approach:

const _ = require('lodash');

let employees = [
  { name: 'Alice', age: 35, department: 'HR', salary: 60000 },
  { name: 'Bob', age: 28, department: 'IT', salary: 70000 },
  { name: 'Charlie', age: 25, department: 'IT', salary: 80000 },
  { name: 'Deborah', age: 45, department: 'Finance', salary: 90000 },
  { name: 'Edward', age: 33, department: 'HR', salary: 75000 },

// Find the average salary of employees in the IT department
let avgSalary = _(employees)
  .filter(emp => emp.department === 'IT')
  .map(emp => emp.salary)
console.log(avgSalary); // Output: 75000

// Find the names of the top 2 highest-paid employees
let topPaidEmployees = _(employees)
  .sortBy(emp => -emp.salary)
  .map(emp =>
console.log(topPaidEmployees); // Output: ['Deborah', 'Charlie']

In this example, chaining and lazy evaluation allows for more readable and efficient code. The operations are sequenced, and only the necessary computations are performed.

Tips and Best Practices

Here are some tips and best practices for using chaining and lazy evaluation in Lodash:

  1. Use chaining for readability: Chaining can make your code more readable by creating a clear sequence of operations. Use chaining when you have multiple operations on a collection that can be expressed as a pipeline.

  2. Leverage lazy evaluation for performance: Lodash's default lazy evaluation can lead to significant performance improvements. When chaining multiple operations, be mindful of the order in which they are applied. For example, placing a filter() operation before a map() operation can reduce the number of elements that need to be mapped.

  3. Know when to use value(): To invoke the chain and get the final result, call the value() method on the lazy wrapper. Be aware that invoking any non-chainable method or array method will implicitly call value() and end the chain.

  4. Use explicit chaining when needed: If you need to chain methods on an object that is not an array or a collection, you can use the _.chain() method to create an explicit chain. However, this is less common and not necessary for most use cases.

  5. Know when not to use chaining: While chaining and lazy evaluation can lead to more readable and efficient code, they are not always the best solution for every problem. If you have a single operation on a collection or if chaining would make your code less clear, consider using individual Lodash functions instead.

In conclusion, chaining and lazy evaluation are powerful features of Lodash that can help you write more efficient and readable code. By understanding these concepts and following the best practices outlined above, you can unlock the full potential of Lodash in your JavaScript projects.

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