Compare Arrays in JavaScript

Compare Arrays in JavaScript

Compare Arrays in JavaScript

In this post, we will give you information about Compare Arrays in JavaScript. Here we will give you detail about Compare Arrays in JavaScript And how to use it also give you a demo for it if it is necessary.

Arrays are objects in JavaScript, so the triple equals operator===
only returns true if the arrays are the same reference.

const a = [1, 2, 3];
const b = [1, 2, 3];

a === a; // true
a === b; // false

How do you compare whether two arrays are equal? Equality is a tricky
subject: the JavaScript spec defines 4 different ways of checking if two values are “equal”, and that doesn’t take into account deep equality between objects.

In cases like this, it helps to be as explicit as possible about what
you mean by “equal.” In software engineering, asking
a question in the right way often makes the answer obvious.

With that in mind, here’s 3 definitions of equality for arrays and
how to check them.

Same Length, Each Value Equal for Compare Arrays in JavaScript

One approach for comparing a and b is checking if each value of a
is strictly equal to the corresponding value of b. This works well
if all the elements of the arrays are primitives as opposed to objects.

const a = [1, 2, 3];
const b = [4, 5, 6];
const c = [1, 2, 3];

function arrayEquals(a, b) {
  return Array.isArray(a) &&
    Array.isArray(b) &&
    a.length === b.length &&
    a.every((val, index) => val === b[index]);

arrayEquals(a, b); // false
arrayEquals(a, c); // true

Deep Equality With POJOs

The previous arrayEquals() function works great for primitive values,
but falls short if you want to compare objects by value.

const a = [{ answer: 42 }, { powerLevel: 9001 }];
const b = [{ answer: 42 }, { powerLevel: 9001 }];

// false, because { answer: 42 } !== { answer: 42 }, different references
arrayEquals(a, b);

One neat way to take into account object values is comparing arrays
by their JSON.stringify() output.

const a = [{ answer: 42 }, { powerLevel: 9001 }];
const b = [{ answer: 42 }, { powerLevel: 9001 }];
const c = [{ answer: 42 }, { password: 'taco' }];

JSON.stringify(a) === JSON.stringify(b); // true
JSON.stringify(a) === JSON.stringify(c); // false

This approach is handy because it requires minimal code and no outside
libraries. However, comparing JSON.stringify() output has an unfortunate
edge case that may be a problem depending on your use case. Since undefined
isn’t a valid JSON value, the below arrays have the same JSON.stringify() output,
because JSON.stringify() converts undefined to null.

const a = [undefined];
const b = [null];

Using Lodash’s isEqual()

In addition to the null vs undefined quirk, comparing JSON.stringify()
output also doesn’t take into account object types. As far as JSON.stringify()
is concerned, an object with a toJSON() function that returns 42 is the same
as the number 42.

const a = [{ toJSON: () => 42 }];
const b = [42];

JSON.stringify(a); // '[42]'
JSON.stringify(b); // '[42]'

Similarly, a custom object is the same as a POJO:

class MyClass {
  constructor(obj) {
    Object.assign(this, obj);

const a = [new MyClass({ answer: 42 })];
const b = [{ answer: 42 }];

JSON.stringify(a) === JSON.stringify(b); // true

Lodash’s isEqual() function, on the other hand,
takes all this into account.

const _ = require('lodash');

class MyClass {
  constructor(obj) {
    Object.assign(this, obj);

const a = [new MyClass({ answer: 42 })];
const b = [{ answer: 42 }];

_.isEqual(a, b); // false

Lodash’s isEqual() function is the way to go if you need all the bells and whistles of checking that objects have the same class. The JSON.stringify()approach works well for POJOs, just make sure you take into account nullĀ and only use it with trusted data – toJSON() can be a security vulnerability.

JavaScript Fundamentals for Compare Arrays in JavaScript

JavaScript is a programming language that is used to create interactive web pages. It is a client-side scripting language, which means that it runs on the user’s browser. JavaScript can be used to add animation, interactivity, and functionality to web pages.

Here are some of the fundamentals of JavaScript:

  • Variables: Variables are used to store data. They are declared using the var keyword.
  • Data types: JavaScript has a variety of data types, including strings, numbers, booleans, objects, and arrays.
  • Operators: Operators are used to perform operations on data.
  • Control flow statements: Control flow statements allow you to control the order in which your code is executed.
  • Functions: Functions are blocks of code that can be reused.
  • Objects: Objects are used to store data in key-value pairs.
  • Arrays: Arrays are used to store data in a sequential order.
  • Events and event handlers: Events are notifications that are sent by the browser when something happens, such as when the user clicks on an element or moves the mouse over an element. Event handlers are functions that are called in response to an event.
  • DOM manipulation: The Document Object Model (DOM) is a tree-like structure that represents the elements of a web page. JavaScript can be used to manipulate the DOM to change the appearance or behavior of a web page.

These are just some of the fundamentals of JavaScript. There are many other concepts that you can learn as you continue to develop your skills.

Here are some resources that you can use to learn more about JavaScript:

  • Mozilla Developer Network (MDN): The MDN is a great resource for learning about JavaScript. It has a comprehensive reference guide, tutorials, and articles on a wide range of topics.
  • W3Schools: W3Schools is another great resource for learning about JavaScript. It has interactive tutorials and quizzes that can help you learn the basics of the language.
  • is a website that provides in-depth tutorials on JavaScript. It also has a forum where you can ask questions and get help from other JavaScript developers.

I hope this helps for Compare Arrays in JavaScript!

Here are some additional tips for learning JavaScript:

  • Start with the basics: Before you start trying to build complex applications, it’s important to learn the basics of JavaScript. This includes things like variables, data types, operators, and control flow statements.
  • Practice regularly: The best way to learn JavaScript is to practice regularly. Try to find some time each day to work on JavaScript projects.
  • Get help from others: If you get stuck, don’t be afraid to ask for help from others. There are many online forums and communities where you can get help from other JavaScript developers.

With a little practice, you’ll be able to learn JavaScript and start building amazing web applications.

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