the requested PHP extension dom is missing from your system. code example

Example 1: phpunit/phpunit 7.5.20 requires ext-dom * -> the requested PHP extension dom is missing from your system.

//First of all, read the warning! It says do not run composer as root! Secondly, you're probably using Xammp on your local which has the required php libraries as default.
// But in your server you're missing ext-dom. php-xml has all the related packages you need. So, you can simply install it by running:

sudo apt-get update
sudo apt install php-xml


//Most likely you are missing mbstring too. If you get the error, install this package as well with:

sudo apt-get install php-mbstring

//Then run:
composer update
composer require cviebrock/eloquent-sluggable

Example 2: - The requested PHP extension ext-http * is missing from your system. Install or enable PHP's http extension.

find "ext-http": "*" in  composer.json and remve it