How do browsers render html

They follow standards because it allows websites to behave the same way across all browsers, and creates less work and fewer headaches for web developers. The rendering engine has a very important job as it displays what you see on your screen. It communicates with the networking layer of the browser to grab HTML code and other items passed from a remote server. Then it follows these steps:. It is a tree like structure made out of the HTML, where each tag is a branch starting at the root element.

Layout Process — Once the render tree is constructed, the rendering engine recursively goes through the HTML elements in the tree and figure out where they should be placed on the screen. This starts at the top left in position 0,0 and elements and attributes are mapped to coordinates on the screen.

Painting — Each node branch of the render tree is drawn out on the screen by communicating with the Operating System Interface which contains designs and styles for how UI elements should look. For Google to understand that a word on the page is in the body context of the page, it must be able to process the entire page.

JavaScript is a programming language which allows things to happen inside of the browser and makes web pages interactive.

Things like popup windows, actions that occur on a button press and elements that move across the page are all things done by JavaScript. This means that JavaScript code executes after the web page has been rendered and painted onto the screen, and when it executes it triggers a re-render to account for changes made. But: Today, while watching a different page of mine that spits out a line by line status of a long-running job, it occurred to me that that page flushes after each line and the browser renders that incrementally as desired.

This doesn't match my conclusion from above and now I don't know what the rules are. Is there a predictable way to do this? Does it vary per browser? This question doesn't necessarily have anything to do with Javascript. If I understand you correctly, you want a "loading"-image to display whilst page is still loading up content.

You can place this div elsewhere with help of some css. Then have Jquery remove this div when page is loaded. Other than the built in delay for Firefox, there are other areas which cause the browser to wait before rendering. As an html page is sent to the browser it first has to decide where things go before it can draw the screen.

For example, tables are notorious for causing rendering delays. In order to draw a table the browser needs to compute column sizes.

If you use percentages as column widths or don't specify them at all, then the browser has to get the entire table before rendering. However, if you use something like the table-layout: fixed; css attribute then the browser can just read the first row and start drawing as data is fed to it. Other tags can cause similar issues.

Basically any time the browser has to compute the size of content, then it has to have all of the content to render. As a self-imposed rule, I never let the browser determine anything. Instead I give my elements fixed sizes. As a result the sites I work on usually have lightning fast rendering. My original answer should be useful to someone I hope , but it isn't a direct response to the question, so I'll post another answer.

The answer to your restated question is "no". In the case of FF, there is a predefined initial render delay, but other browsers will be different. That FF render delay can be tweaked as well. Using FF as an example, those initial ms are time for FF to find out at least some useful information before attempting the first render. It then does additional renders periodically as it learns more. To directly answer your question, I believe Firefox waits ms before acting on the first data received, but that can be changed.

For other browsers, I don't know. Before then, any attempt to use jQuery will fail. In other words, your spinner isn't showing up because jQuery isn't ready to process that request yet. Consider the following example, where two placeholders are shown on-screen, and we'll use jQuery to hide them. Now that we have that out of the way, the solution to the larger problem the "right way" is AJAX. I expect it will vary by browser: some will start to render before the page is completely received; others will wait for the whole html file before starting.

I note that the HTTP Response specification provides a " Partial Content" header which might offer some hope for a cross-browser solution which is worth looking into. There's almost certainly a number of ways to cut it, but my immediate idea would be to deliver the stub page, then use ajax to pull and render the fragments on demand. I can't imagine this being too hard to implement; even with coldfusion. You start the spinner when you fire the ajax request and stop it when the callback is invoked.

Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? A bunch of characters in a text file does not do the browser engine a lot of good.

Without this tokenization process, the bunch of characters will just result in a bunch of meaningless text, i. When you save a file with the. The way the browser interprets this file is by first parsing it. In the parsing process, and particularly during tokenization, every start and end HTML tag in the file is accounted for. The parser understands each string in angle brackets e.

For example, a token that represents an anchor tag will have different properties from one that represents a paragraph token. Conceptually, you may see a token as some sort of data structure that contains information about a certain HTML tag. Essentially, an HTML file is broken down into small units of parsing called tokens. Upon creating these nodes, the nodes are then linked in a tree data structure known as the DOM. The DOM establishes the parent-child relationships, adjacent sibling relationships, etc.

The relationship between every node is established in this DOM object. No — you open the HTML file, most times in the form index. This is exactly why you do so: the browser must go through transforming the raw bytes of HTML data into the DOM before anything can happen.

No matter how small, it does take some time, regardless of the file size. While the browser receives the raw bytes of data and kicks off the DOM construction process, it will also make a request to fetch the main. As you may have guessed, the browser also receives the raw bytes of CSS data, whether from the internet or your local disk. But what exactly is done with these raw bytes of CSS data?

In other words, the raw bytes of data are converted to characters, then tokenized. Nodes are also formed, and, finally, a tree structure is formed. What is a tree structure? This has to be converted to a form it recognizes — and that happens to be these tree structures. CSS has something called the cascade. The cascade is how the browser determines what styles are applied to an element.

Because styles affecting an element may come from a parent element i. This is because the browser has to recursively go through the CSS tree structure and determine the styles that affect a particular element. All well and good. Can we have something rendered to the screen now? Note that if an element has been hidden by CSS e. The hidden element will be present in the DOM but not the render tree.

With the render tree constructed, the next step is to perform the layout. Well, first, the browser has to calculate the exact size and position of each object on the page. This mathematician then figures out the exact position and size of each element with the browser viewport.

Finally, the elements are now rendered to the screen! When you hear render blocking, what comes to mind? The point is, you should get your HTML and CSS to the client as soon as possible to optimize the time to the first render of your applications. A decent web application will definitely use some JavaScript. A basic HTML page rendered. A simple text and image are rendered on the screen.

From previous explanations, the browser reads raw bytes of the HTML file from the disk or network and transforms that into characters.

The characters are further parsed into tokens. What happens to this flow once we introduce JavaScript? Well, one of the most important things to remember is that whenever the browser encounters a script tag, the DOM construction is paused!