I need to edit a codes such as footer and social media link. I have a total of 10 webpages. I need to find out a way on how can edit a code in all the pages at the same time. I have uses Toolbox Plugin of notepad++ but it was not very useful. Is there any easier way to do that. How do big companies handle such issues?
If you have a lot of repetition, use a template engine and its CLI to generate you static HTML.
For example Pug.
In addition to @maruru answer is Server Side Includes
<!--#include file="footer.html" -->
It's not recommended to do that anymore as it can be a security risk, but you can give it a try without needing PHP, JS or other.
If you only have HTML files with no preprocessor, CMS (Content Management System) or the like, you are most likely out of luck and you will have to edit all files individually. If I had to do so, I would most likely write a quick and dirty script (NodeJS in my case) which searches all files in a directory for a given string and replaces that string with another given string (alternatively use DOM tools for a better script and better results).
Big companies do not just write HTML files, they usually use a CMS or HTML generator. For small sites, PHP (PHP Hypertext Preprocessor) is a nice tool/language to write separate partials and include them into your content sites. If you do not have the server-capabilities to even run PHP, WebComponents might be the solution for you (at the moment, they still need polyfills!).
PHP Example
<!-- footer.html --> <div class=footer> (c) Rajat </div><!DOCTYPE HTML> <!-- Some other file --> <title>Rajat's Site</title> <div class=content>Welcome to my website! Some text here<div> <?php include('footer.html'); ?>Polymer (WebComponents) Example
<!-- my-footer.html --> <link rel="import" href="bower_components/polymer/polymer.html"> <dom-module id="my-footer"> <!-- Defines the element's style and local DOM --> <template> <style> :host { display: block; } </style> <div class=footer>(c) Rajat</div> </template> <!-- Creates the element's prototype and registers it --> <script> Polymer({ is: 'my-footer' }); </script> </dom-module><!DOCTYPE HTML> <!-- Main file --> <title>Rajat's Site</title> <script src="polygit.org/components/webcomponentsjs/webcompone…"></script> <link rel="import" href="webcomponents/my-footer.html"> <div class=content>Welcome to my website! Some text here<div> <my-footer></my-footer>