Why do We Use index.html Files?

Photo by Taylor Vick on Unsplash

TLDR: An index.html is the default file web servers look for when serving a home page for a website. These files are stored at the root of the server’s directory structure and this pattern has been expanded to other technologies including ES6 module imports.

Setting up or managing websites raises many questions commonly answered with “That is just how it is done.” Some of the most common questions for setting up a website are what an index.html file is, why they must use that name, and why the file must be placed in a specific location on the hosting server. There is more to using the name than “it is just how it is done,” so let us discuss what is behind the naming convention and why we use index.html files.

What is an index.html File?

Let us start with the name. Using index.html for the file name follows an agreed-upon web standard by software engineers to use a common file name on servers. The index is the root or starting point of your website. This naming policy is crucial for web development as it ensures website builders have uniform experiences with the servers they work on.

This index.html has to be placed in a specific location on the server. For the index.html file to work correctly, it must be placed in the top-level directory on the server. This top-level directory is often called the root directory and has a relative path of “/.” To follow this requirement, you must push your index.html into the top-level directory.

Website URLs mirror the structure of their hosting server’s architecture. Each new slash and set of words of a URL indicates another level of the subdirectory that you are navigating into:

Figure 1. Diagram of the components of a URL provided by HubSpot.

The root directory or “/“ indicates that you are in the home directory and is the first location the server looks at when you visit a homepage. When you enter a URL without any path or query parameter you are telling the server to return the index.html file at the root of the server’s file structure:

Figure 2. Showing URL entered by user and how the server interprets the URL.

When you enter this address, the server automatically looks for the index.html file to return to the user. Of course, you can configure your server to look for other files. You could set the default “/“ route to return home.html or anything else that makes sense for your team, but this requires extra configuration on the server. It is best to stick with universally accepted practices of using index.html for your homepage’s file.

ES6 Module Imports and Other Extensions of Index

The idea of an index being an entry point into a website has been extended into other programming domains. ES6 introduced the module imports to the JavaScript ecosystem. With module imports, JavaScript allows developers to link and share code between files in their projects using more common import syntax.

One interesting part of ES6 modules is their default import syntax. With ES6 modules you can specify a file or package of code to pull into your file. Or you can specify a directory and let ES6 determine what code to incorporate in your current file.

Here is where ES6 copies the index file logic found in web hosting. If you have a directory with a single file export, but many files, ES6 can link to the index.js file if no file is specified. You can use this to shorten the length of your import statements, making your code shorter and cleaner.

This can be helpful if you are working with a UI component-driven framework like React or Vue and have many support files for a single component file. Instead of extending your import path with a path like “/components/effects/circularSpinner/circularSpinner.js” you can name your export component file index.js and set your import path to “components/effects/circularSpinner.” Much better!