How to slugify a string in JavaScript

A slug is a string that is used to uniquely identify a resource in a URL-friendly way. It is typically used in the URL to identify a specific page or post on a website. A slug consists of a set of characters that are easy to read and remember, and that accurately describe the content of the resource.

A string can be qualified as a slug if it meets the following criteria:

• It consists of lowercase alphanumeric characters (a-z,0-9) and hyphens (-).
• It does not contain any spaces or other special characters.
• It accurately and concisely describes the content of the resource it identifies.
• It is unique within the context of the website or application.

For example, consider the following URL https://byby.dev/react-data-fetching-libraries. In this URL, react-data-fetching-libraries is the slug that identifies the specific blog post.

A simple slugify

In JavaScript, you can slugify a string by converting it to a URL-friendly format where any special characters and spaces are replaced with hyphens or underscores. Here's an example function that can accomplish this:

function slugify(str) {
  str = str.replace(/^\s+|\s+$/g, ''); // trim leading/trailing white space
  str = str.toLowerCase(); // convert string to lowercase
  str = str.replace(/[^a-z0-9 -]/g, '') // remove any non-alphanumeric characters
           .replace(/\s+/g, '-') // replace spaces with hyphens
           .replace(/-+/g, '-'); // remove consecutive hyphens
  return str;
}

const title = "The Quick Brown Fox Jumps Over The Lazy Dog!";
const slug = slugify(title);
console.log(slug); // "the-quick-brown-fox-jumps-over-the-lazy-dog"

Using a library

There are several libraries available in JavaScript that can be used to slugify a string easily without having to write custom code.

• lodash (56k ⭐) — This library provides a wide range of utility functions for JavaScript, including a kebabCase function that can be used to convert a string to kebab case, which is similar to slug format. Kebab case format is a naming convention where words are separated by a hyphen (-) and all letters are in lower case.

const _ = require('lodash');

const myString = 'Hello World';
const kebabCaseString = _.kebabCase(myString);

console.log(kebabCaseString); // Output: hello-world

• Voca (3.5k ⭐) — The Voca library offers helpful functions to make string manipulations comfortable: change case, trim, pad, slugify, latinise, sprintf'y, truncate, escape and much more. In Voca, slugify is a function that converts a string to a URL-friendly slug format.

const { slugify } = require('voca');

const myString = 'Hello World!';
const slugifiedString = slugify(myString);

console.log(slugifiedString); // Output: hello-world

• @sindresorhus/slugify (2.3k ⭐) — Useful for URLs, filenames, and IDs. It handles most major languages, including German (umlauts), Vietnamese, Arabic, Russian, and more.

const slugify = require('@sindresorhus/slugify');

slugify('I ♥ Dogs'); // i-love-dogs
slugify('  Déjà Vu!  '); // deja-vu
slugify('fooBar 123 $#%'); // foo-bar-123
slugify('я люблю единорогов'); // ya-lyublyu-edinorogov

slugify('BAR and baz', {separator: '_'}); // bar_and_baz
slugify('BAR and baz', {separator: ''}); // barandbaz

• slugify (1.2k ⭐) — This library includes a simple slugify function in vanilla ES2015 JavaScript, has no dependencies, coerces foreign symbols to their English equivalent, works in the browser (window.slugify) and AMD/CommonJS-flavored module loaders.

const slugify = require('slugify');

slugify('some string'); // some-string

// if you prefer something other than '-' as separator
slugify('some string', '_');  // some_string

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Comments

[Tracy Gilmore]

Hi Byby,

Was there a reason you used str.replace(/^\s+|\s+$/g, '') rather than using the built-in String.trim() method?

Regards, Tracy

[byby]

Not at all, I just prefer using regex consistently.

[Tracy Gilmore]

Byby, I am a fan of using Regular Expressions but they can be less performant than other options. For instance, using the + symbol to select one or more instances is very open-ended. An alternative, more performant approach might be to replace + with {1,n} where, n is the greatest number of characters you can reasonably expect, there is usually an upper limit. In this case, determining a value for n might be difficult (which demonstrates the problem) so using trim would be a better option.

[Jessica williams]

In JavaScript, you may combine string manipulation and regular expressions to slugify a string. Here is an illustration of a function that turns a string into a slug:

function slugify(str) {
str = str.replace(/^\s+|\s+$/g, ''); // trim leading/trailing spaces
str = str.toLowerCase(); // convert to lowercase
str = str.replace(/[^a-z0-9 -]/g, '') // remove invalid chars
.replace(/\s+/g, '-') // collapse whitespace and replace by "-"
.replace(/-+/g, '-'); // collapse dashes
return str;
}

The following is done by this function:

uses replace() to remove any leading or trailing spaces from the string.

Use toLowerCase() to change the string's case to lowercase.

Uses a regular expression to remove all characters that aren't letters, numbers, spaces, or dashes (/[a-z0-9 -]/g). The g flag instructs the computer to replace every instance, not just the first.

Any whitespace characters (spaces, tabs, and newlines) are combined into a single space, which is then replaced with a dash (-) using the function replace(/s+/g, '-').
Use replace(/-+/g, '-') to combine any consecutive dashes into a single dash.

Here is an illustration of how to use the slugify() function:

const title = "How to slugify a string in JavaScript";
const slug = slugify(title); // "how-to-slugify-a-string-in-javascript"
console.log(slug);