HTML comments are not displayed in the browser, but they can help document your HTML source code.


HTML Entities Some characters are reserved in HTML.
If you use the less than or greater than signs in your text, the browser might mix them with tags.
Character entities are used to display reserved characters in HTML.
A character entity looks like this: 0130260433

HTML Symbol Entities

HTML entities were described in the previous chapter.
Many mathematical, technical, and currency symbols, are not present on a normal keyboard.
To add such symbols to an HTML page, you can use an HTML entity name.
If no entity name exists, you can use an entity number, a decimal, or hexadecimal reference.


YouTube Videos

The easiest way to play videos in HTML, is to use YouTube.
Struggling with Video Formats?
Earlier in this tutorial, you have seen that you might have to convert your videos to different formats to make them play in all browsers.
Converting videos to different formats can be difficult and time-consuming.
An easier solution is to let YouTube play the videos in your web page.
YouTube Video Id
YouTube will display an id (like tgbN6m87vqY), when you save (or play) a video.
You can use this id, and refer to your video in the HTML code.
Playing a YouTube Video in HTML
To play your video on a web page, do the following:
Upload the video to YouTube
Take a note of the video id
Define an iframe element in your web page
Let the src attribute point to the video URL
Use the width and height attributes to specify the dimension of the player


Toggle contextual overlays for displaying lists of links and more with the Bootstrap dropdown plugin. 0130260433

State and Lifecycle

This page introduces the concept of state and lifecycle in a React component. You can find a detailed component API reference here.
Consider the ticking clock example from one of the previous sections. In Rendering Elements, we have only learned one way to update the UI. We call ReactDOM.render() to change the rendered output:


Related Content


Pagination Documentation and examples for showing pagination to indicate a series of related content exists across multiple pages.


CS50 This is CS50x, Harvard University introduction to the intellectual enterprises of computer science and the art of programming for majors and non-majors alike, with or without prior programming experience.
An entry-level course taught by David J. Malan, CS50x teaches students how to think algorithmically and solve problems efficiently. Topics include abstraction, algorithms, data structures, encapsulation, resource management, security, software engineering, and web development. Languages include C, PHP, and JavaScript plus SQL, CSS, and HTML. Problem sets inspired by real-world domains of biology, cryptography, finance, forensics, and gaming.
As of Fall 2015, the on-campus version of CS50x, CS50, was Harvard largest course.


Text/Typography Bootstrap 4 uses a default font-size of 16px, and its line-height is 1.5.
The default font-family is "Helvetica Neue", Helvetica, Arial, sans-serif.
In addition, all p elements have margin-top: 0 and margin-bottom: 1rem (16px by default).


Media object Documentation and examples for Bootstrap’s media object to construct highly repetitive components like blog comments, tweets, and the like.


The Viewport What is The Viewport?
The viewport is the user visible area of a web page.
The viewport varies with the device, and will be smaller on a mobile phone than on a computer screen.
Before tablets and mobile phones, web pages were designed only for computer screens, and it was common for web pages to have a static design and a fixed size.
Then, when we started surfing the internet using tablets and mobile phones, fixed size web pages were too large to fit the viewport.
To fix this, browsers on those devices scaled down the entire web page to fit the screen. This was not perfect!! But a quick fix.


Clearfix Quickly and easily clear floated content within a container by adding a clearfix utility.