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Understanding Repaint and Reflow in JavaScript
Recently, while researching what makes React’s virtual DOM so fast, I realized how little are we aware of javascript performance. So I’m writing this article to help raise awareness about Repaint and Reflow and JavaScript performance in general.”
Before we dig deeper, do we know how a browser works?
A picture is worth a thousand words. So, let’s have a high-level view of how a browser works!
hmm… what’s “browser engine” and “rendering engine”?
The primary job of a browser engine is to transform HTML documents and other resources of a web page into an interactive visual representation on a user’s device.
Besides “browser engine”, two other terms are in common use regarding related concepts: “layout engine” and “rendering engine”. In theory, layout and rendering (or “painting”) could be handled by separate engines. In practice, however, they are tightly coupled and rarely considered separately.
let’s understand how browsers draw a user interface on the screen.
When you hit enter on some link or URL browser make an HTTP request to that page and the corresponding server provides (often) HTML document in response. (a hell lot of things happen in between)
Step by step processing
- The browser parses out the HTML source code and constructs a DOM tree a data representation where every HTML tag has a corresponding node in the tree and the text chunks between tags get a text node representation too. The root node in the DOM tree is the
documentElement(the<html>tag) - The browser parses the CSS code, makes sense of it. The styling information cascades: the basic rules are in the User-Agent stylesheets (the browser defaults), then there could be user stylesheets, author (as in the author of the page) stylesheets - external, imported, inline, and finally styles that are coded into the
styleattributes of the HTML tags - Then comes the interesting part — constructing a render tree. The render tree is sort of like the DOM tree but doesn’t match it exactly. The render tree knows about styles, so if you’re hiding a
divwithdisplay: none, it won’t be represented in the render tree. Same for the other invisible elements, likeheadand everything in it. On the other hand, there might be DOM elements that are represented with more than one node in the render tree-like text nodes for example where every line in a<p>needs a render node. A node in the render tree is called a frame, or a box (as in a CSS box, according to the box model). Each of these nodes has the CSS box properties - width, height, border, margin, etc - Once the render tree is constructed, the browser can paint (draw) the render tree nodes on the screen
Here is a snapshot of how browser draws user interface on the screen.
It happens in the fraction of seconds that we don’t even notice that all this happened.
Look closely.
How browser drawing the layout and trying to detect root element, siblings and it’s child element as a node comes and rearranging it’s layout accordingly.
Let’s take one example
<html>
<head>
<title>Repaint And Reflow</title>
</head>
<body>
<p>
<strong>How's The Josh?</strong>
<strong><b> High Sir...</b></strong>
</p>
<div style="display: none">
Nothing to display
</div>
<div><img src="..." /></div>
...
</body>
</html>
The DOM tree that represents this HTML document basically has one node for each tag and one text node for each piece of text between nodes (for simplicity let’s ignore the fact that whitespace is text nodes too) :
documentElement (html)
head
title
body
p
strong
[text node]
p
strong
b
[text node]
div
[text node]
div
img
...
The render tree would be the visual part of the DOM tree. It is missing some stuff — the head and the hidden div, but it has additional nodes (aka frames, aka boxes) for the lines of text.
root (RenderView)
body
p
line 1
line 2
line 3
...
div
img
...
The root node of the render tree is the frame (the box) that contains all other elements. You can think of it as being the inner part of the browser window, as this is the restricted area where the page could spread. Technically WebKit calls the root node RenderView and it corresponds to the CSS initial containing block, which is basically the viewport rectangle from the top of the page (0, 0) to (window.innerWidth, window.innerHeight)
Figuring out what and how exactly to display on the screen involves a recursive walk down (a flow) through the render tree.
#react #javascript #web-development #proramming #developer
What is GEEK
Buddha Community
1589255577
The essential JavaScript concepts that you should understand
As a JavaScript developer of any level, you need to understand its foundational concepts and some of the new ideas that help us developing code. In this article, we are going to review 16 basic concepts. So without further ado, let’s get to it.
#javascript-interview #javascript-development #javascript-fundamental #javascript #javascript-tips
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What is JavaScript - Stackfindover - Blog
Who invented JavaScript, how it works, as we have given information about Programming language in our previous article ( What is PHP ), but today we will talk about what is JavaScript, why JavaScript is used The Answers to all such questions and much other information about JavaScript, you are going to get here today. Hope this information will work for you.
Who invented JavaScript?
JavaScript language was invented by Brendan Eich in 1995. JavaScript is inspired by Java Programming Language. The first name of JavaScript was Mocha which was named by Marc Andreessen, Marc Andreessen is the founder of Netscape and in the same year Mocha was renamed LiveScript, and later in December 1995, it was renamed JavaScript which is still in trend.
What is JavaScript?
JavaScript is a client-side scripting language used with HTML (Hypertext Markup Language). JavaScript is an Interpreted / Oriented language called JS in programming language JavaScript code can be run on any normal web browser. To run the code of JavaScript, we have to enable JavaScript of Web Browser. But some web browsers already have JavaScript enabled.
Today almost all websites are using it as web technology, mind is that there is maximum scope in JavaScript in the coming time, so if you want to become a programmer, then you can be very beneficial to learn JavaScript.
JavaScript Hello World Program
In JavaScript, ‘document.write‘ is used to represent a string on a browser.
<script type="text/javascript">
document.write("Hello World!");
</script>
How to comment JavaScript code?
- For single line comment in JavaScript we have to use // (double slashes)
- For multiple line comments we have to use / * – – * /
<script type="text/javascript">
//single line comment
/* document.write("Hello"); */
</script>
Advantages and Disadvantages of JavaScript
#javascript #javascript code #javascript hello world #what is javascript #who invented javascript
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Hire Dedicated JavaScript Developers -Hire JavaScript Developers
It is said that a digital resource a business has must be interactive in nature, so the website or the business app should be interactive. How do you make the app interactive? With the use of JavaScript.
Does your business need an interactive website or app?
Hire Dedicated JavaScript Developer from WebClues Infotech as the developer we offer is highly skilled and expert in what they do. Our developers are collaborative in nature and work with complete transparency with the customers.
The technology used to develop the overall app by the developers from WebClues Infotech is at par with the latest available technology.
Get your business app with JavaScript
For more inquiry click here https://bit.ly/31eZyDZ
Book Free Interview: https://bit.ly/3dDShFg
#hire dedicated javascript developers #hire javascript developers #top javascript developers for hire #hire javascript developer #hire a freelancer for javascript developer #hire the best javascript developers
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JS Development Company India | JavaScript Development Services
PixelCrayons: Our JavaScript web development service offers you a feature-packed & dynamic web application that effectively caters to your business challenges and provide you the best RoI. Our JavaScript web development company works on all major frameworks & libraries like Angular, React, Nodejs, Vue.js, to name a few.
With 15+ years of domain expertise, we have successfully delivered 13800+ projects and have successfully garnered 6800+ happy customers with 97%+ client retention rate.
Looking for professional JavaScript web app development services? We provide custom JavaScript development services applying latest version frameworks and libraries to propel businesses to the next level. Our well-defined and manageable JS development processes are balanced between cost, time and quality along with clear communication.
Our JavaScript development companies offers you strict NDA, 100% money back guarantee and agile/DevOps approach.
#javascript development company #javascript development services #javascript web development #javascript development #javascript web development services #javascript web development company
1600510680
Definitive Guide to Understand Javascript Array reduce()
Javascript array reduce() is an inbuilt method that is used to apply a function to each element in the array to reduce the array to a single value. The reduce() function executes the provided function for each value of an array from left-to-right. The return value of a function is stored in an accumulator.
Understanding Javascript array reduce()
JavaScript array reduce() is one of the pioneer function of functional programming. The reduce() method accepts two parameters, the total and the current value. If you want to add all the values of an array, then use the array reduce() function.
It is similar to both Javascript map() and Javascript filter() but, it differs in the callback arguments.
The callback now receives an accumulator (it accumulates all the return values. Its value is the accumulation of a previously returned accumulations), a current value, a current index, and finally, the whole array.
#javascript #javascript map #javascript filter #javascript array reduce