Understanding JavaScript Fundamentals: Your Cheat Sheet

JavaScript is a posh matter that may be extraordinarily tough to get a deal with on.

However, it has by no means been extra necessary to know it as a result of JavaScript is turning into more and more prevalent on the web sites that we handle.

As the trendy internet continues to evolve, JavaScript utilization continues to rise.

website positioning professionals could lengthy for occasions passed by when web sites have been static and coded solely in HTML and CSS. However, participating web sites usually require interactivity, which is often powered by JavaScript.

HTTP Archive graph showing increase in JavaScript bytes across the webThe variety of JavaScript bytes throughout your complete internet has elevated by 35 p.c on desktop and 62.7 p.c on cellular during the last three years.

As Google Webmaster Trends Analyst John Mueller put it: JavaScript is “not going away.”

This programming language is throughout us, so we should always get higher acquainted with it. Let’s be proactive and be taught extra about JavaScript moderately than fearing it.

There is commonly a false impression that JavaScript is solely for builders to fret about.

I might argue that this isn’t the case, as it may possibly trigger an issue for anybody who needs clients and serps to have the ability to entry their web site’s content material.

If you aren’t fully aware of JavaScript, and even have completely no thought what it’s or does, don’t fear.

I’ve put collectively a glossary of the important thing phrases and basic ideas it’s best to know that will help you get began in your journey of discovery.

What Is JavaScript?

JavaScript is a programming language that lets you implement advanced options on a web site, similar to dynamic parts or interactivity.

JavaScript is executed as soon as the knowledge from the HTML and CSS within the supply code has been parsed and constructed.

The JavaScript will then set off any occasions or variables specified inside it, the Document Object Model (DOM) will likely be up to date, and, lastly, the JavaScript will likely be rendered within the browser.

The HTML and CSS will usually kind the foundations of a web page’s construction, and any JavaScript will make the ultimate tweaks and alterations.

Document Object Model (DOM)

The Document Object Model (DOM) is created when a web page is loaded, and it’s made up of nodes and objects which map out the entire completely different parts and attributes on a web page.

The web page is mapped out on this means in order that different packages can modify and manipulate the web page when it comes to its construction, content material, and styling.

An example diagram showing how a Document Object Model is laid out

Altering the weather of a web page’s DOM is feasible by utilizing a language like JavaScript.


ECMAScript (ES) is a scripting language that was created to standardize using JavaScript code.

Different editions of ECMAScript are launched when the language is up to date and tweaked over time, similar to ES5 and ES6 (which can be known as ES2015).


A transpiler is a software that transforms supply code into a unique programming language. The idea is a bit like Google Translate, however for code.

You can convert a selected supply language into a unique goal language, for instance, JavaScript to C++ or Python to Ruby.

With regard to JavaScript rendering notably, a transpiler is commonly really helpful for remodeling ES6 into ES5 as a result of Google at present makes use of an outdated model of Chrome for rendering which doesn’t but help ES6.

Chrome 41

When rendering pages, Google makes use of an online rendering service which relies on Chrome 41. This implies that Google’s rendering engine helps the identical options and functionalities of that specific model of Chrome.

When you contemplate that essentially the most up-to-date model is Chrome 71, you possibly can see that many variations have been launched since Chrome 41 went reside in 2015, and all of those variations got here with new options. This is why Google’s rendering service at present helps ES5 moderately than the later ES6 model of the language.

Single-page Application (SPA)

A single-page software (SPA) is a web site or internet app that dynamically re-writes and re-renders a web page as a consumer interacts with it, moderately than making separate requests to the server for brand new HTML and content material.

JavaScript frameworks can be utilized to help the dynamically altering parts of SPAs.

Angular, Polymer, React & Vue

These are all several types of JavaScript frameworks.

  • Angular and Polymer have been developed by Google.
  • React was developed by Facebook.
  • Vue was developed by Evan You, who used to work on Google’s Angular group.

Angular, Polymer, React and Vue JavaScript framework logos

Each JavaScript framework has its personal execs and cons, so builders will select to work with the one which most closely fits them and the undertaking they’re engaged on.

If you wish to be taught extra about how the completely different frameworks measure up, this information provides an in depth comparability.

JavaScript Rendering

JavaScript rendering includes taking the script and the directions it accommodates, processing all of it, then operating it in order that the required output is proven within the browser. There are many various strategies you should use to manage the way in which through which JavaScript is rendered.

Requiring JavaScript to be rendered on a web page can negatively affect two key areas:

  • Site pace
  • Search engine crawling and indexing

Depending on which rendering technique you employ, you possibly can scale back web page load pace and ensure content material is accessible to serps for crawling and indexing.


Pre-rendering includes rendering the content material on a web page earlier than it’s requested by the consumer or search engine, in order that they obtain a static web page with the entire content material on there able to go.

By preloading a web page on this means, it implies that your content material will likely be accessible moderately than a search engine or consumer’s browser having to render the web page themselves.

Pre-rendering is often used for search engine bots moderately than people. This is as a result of a static, pre-rendered web page will likely be much less participating for customers as it’ll lack any dynamic content material or interactivity.

Server-side Rendering

The internet hosting server does the heavy lifting and renders the web page in order that the JavaScript has already been processed and the content material is able to be handed over to the consumer’s browser or search engine crawler when it’s requested.

Server-side rendering

This technique helps to scale back any pressure on the consumer’s system that might have been brought on by processing JavaScript, and this may enhance web page load pace.

Server-side rendering additionally ensures the complete content material may be seen and listed by serps.

Client-side Rendering

During client-side rendering, JavaScript is processed by the consumer’s browser or by the search engine that’s requesting a web page.

The server will deal with the preliminary request, however the remainder of the work of processing and rendering a web page falls on the consumer’s system or the search engine.

Client-side rendering

It is commonly suggested in opposition to to make use of client-side rendering as there’s a delay between Google crawling pages after which having the ability to render them.

Google places pages that should be rendered right into a queue till sufficient sources turn out to be accessible to course of them.

If you’re counting on Google to render a web page client-side, this may delay indexing by as much as every week after it’s initially crawled.

Dynamic Rendering

Dynamic rendering includes utilizing completely different rendering strategies relying on whether or not a consumer’s browser or a search engine bot is requesting a web page.

If your website often renders client-side, when Googlebot is detected the web page will likely be pre-rendered utilizing a mini client-side renderer (for instance, Puppeteer or Rendertron), so the content material may be seen and listed immediately.

Dynamic rendering

Hybrid Rendering

Hybrid rendering includes a mixture of each server-side rendering and client-side rendering.

The core content material is pre-rendered server-side and despatched to the shopper, whether or not that’s the consumer’s browser or the search engine crawler that’s requesting the content material.

After the web page is initially loaded, extra JavaScript for any interactivity is then rendered client-side.

Hybrid rendering


Hopefully you discovered this information helpful, and that it helped you higher perceive the fundamentals of JavaScript and the way it impacts web sites.

Now that you just’ve brushed up on the important thing phrases, you have to be higher geared up to carry your personal in conversations with the builders!

More Resources:

Image Credits

Featured Image: Unsplash
In-Post Image #1: HTTP Archive
In-Post Image #2: Computer Hope
All screenshots taken by writer, January 2019

Subscribe to SEJ

Get our each day publication from SEJ’s Founder Loren Baker in regards to the newest information within the trade!


Tags: , , , ,