Css in javascript with jss and react

Learning Speed

In this tutorial, the learning speed is your choice.

Everything is up to you.

If you are struggling, take a break, or re-read the material.

Always make sure you understand all the «Try-it-Yourself» examples.

The only way to become a clever programmer is to: Practice. Practice. Practice. Code. Code. Code !

Commonly Asked Questions

  • How do I get JavaScript?
  • Where can I download JavaScript?
  • Is JavaScript Free?

You don’t have to get or download JavaScript.

JavaScript is already running in your browser on your computer, on your tablet, and on your smart-phone.

JavaScript is free to use for everyone.

JavaScript References

W3Schools maintains a complete JavaScript reference, including all HTML and browser objects.

The reference contains examples for all properties, methods and events, and is continuously updated according to the latest web standards.

Complete JavaScript Reference »

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JS Tutorial

JS HOMEJS IntroductionJS Where ToJS OutputJS StatementsJS SyntaxJS CommentsJS VariablesJS OperatorsJS ArithmeticJS AssignmentJS Data TypesJS FunctionsJS ObjectsJS EventsJS StringsJS String MethodsJS NumbersJS Number MethodsJS ArraysJS Array MethodsJS Array SortJS Array IterationJS DatesJS Date FormatsJS Date Get MethodsJS Date Set MethodsJS MathJS RandomJS BooleansJS ComparisonsJS ConditionsJS SwitchJS Loop ForJS Loop WhileJS BreakJS Type ConversionJS BitwiseJS RegExpJS ErrorsJS ScopeJS HoistingJS Strict ModeJS this KeywordJS LetJS ConstJS Arrow FunctionJS DebuggingJS Style GuideJS Best PracticesJS MistakesJS PerformanceJS Reserved WordsJS VersionsJS Version ES5JS Version ES6JS JSON

Window Size

Two properties can be used to determine the size of the browser window.

Both properties return the sizes in pixels:

  • — the inner height of the browser window (in pixels)
  • — the inner width of the browser window (in pixels)

The browser window (the browser viewport) is NOT including toolbars and scrollbars.

For Internet Explorer 8, 7, 6, 5:

  • or

A practical JavaScript solution (covering all browsers):


var w = window.innerWidth|| document.documentElement.clientWidth|| document.body.clientWidth;var h = window.innerHeight|| document.documentElement.clientHeight|| document.body.clientHeight;

The example displays the browser window’s height and width: (NOT including toolbars/scrollbars)

CSS injection order

The CSS injected by Material-UI to style a component has the highest specificity possible as the is injected at the bottom of the to ensure the components always render correctly.

You might, however, also want to override these styles, for example with styled-components. If you are experiencing a CSS injection order issue, JSS to handle this situation. By adjusting the placement of the within your HTML head you can that the CSS rules are applied to your components.

Other HTML element

Create React App strips HTML comments when creating the production build. To get around the issue, you can provide a DOM element (other than a comment) as the JSS insertion point.

For example, a element:

Definition and Usage

The style property returns a CSSStyleDeclaration object, which represents an element’s style attribute.

The style property is used to get or set a specific style of an element using different CSS properties.

Note: It is not possible to set styles by assigning a string to the style property, e.g. element.style = «color: red;». To set the style of an element, append a «CSS» property to style and specify a value, like this:

element.style.backgroundColor = «red»;   // set the background color of an element to redTry it

As you can see, the JavaScript syntax for setting CSS properties is slightly different than CSS (backgroundColor instead of background-color).

For a list of all available properties, see our Style Object Reference.

Note: The style property only returns the CSS declarations set in the element’s inline style attribute, e.g. <p style=»color: red;»>. It is not possible to use this property to get information about style rules from the <head> section in the document or external style sheets.

However, you can access the <style> element from <head> by using document.getElementsByTagName():

var x = document.getElementsByTagName(«STYLE»);   // get the first <style> element Try it

Note: It is recommended to use the style property instead of the element.setAttribute(«style», «…») method, because the style property will not overwrite other CSS properties that may be specified in the style attribute.

Server side rendering

If you are wondering about this feature, it is completely supported. Some may say because you are generating the CSS in runtime and you need to download, parse and run the JavaScript before seeing something on the screen with design, well, you can generate it in the server and it would be a lot faster.

Because only the critical parts of CSS are used in a page, you don’t need to send the whole bundle with the three hundred components styles of your app. Only the styles used are generated and sent. And if you are not using React, JSS is framework agnostic so you can implement your own system.

Wow! All those features are pretty neat.

Типы файлов JSS

Ассоциация основного файла JSS


Формат файла: .jss
Тип файла: JavaScript Style Sheet File

JavaScript Файл стилей обеспечивает большую гибкость для определения различных стилей для веб-страниц, созданных с помощью JSS (Sheets JavaScript Style), который является языком таблицы стилей технологии.

Создатель: SourceForge
Категория файла: Веб-файлф
Ключ реестра: HKEY_CLASSES_ROOT\.jss

Программные обеспечения, открывающие JavaScript Style Sheet File:

JSS (Javascript Style Sheets), разработчик — SourceForge

Совместимый с:


Ассоциации других файлов JSS


Формат файла: .jss
Тип файла: JACOsub Subtitle File

JACOsub Файл субтитров используются для хранения видео субтитров в текстовом формате. Кроме того, это позволяет сохранить временные последовательности для отображения текста или графических субтитров. JSS файл, созданный программным обеспечением JACOsub субтитров.

Создатель: Open Source
Категория файла: Видео файлы

Программы, открывающие файлы JACOsub Subtitle File :

MPlayer, разработчик — The MPlayer Team

Совместимый с:


URUWorks Subtitle Workshop, разработчик — URUWORKS

Совместимый с:



Формат файла: .jss
Тип файла: JAWS Script File

Файл сценария, связанный с JAWS, считывающим экран программного обеспечения для Microsoft Windows. Файл JSS содержит функции, которые используются в процессе чтения текста на экране.

Создатель: Freedom Scientific
Категория файла: Файлы разработчика

Программы, открывающие файлы JAWS Script File :

JAWS, разработчик — Freedom Scientific

Совместимый с:


Points of Interest

While it seems that user scripts and styles have a finite shelf life, the beauty of open source ensures that anyone can revive a JS or CSS and bring it back to the community.

Apart from the above-mentioned sites, greasyfork.org also provides user scripts. For a long time, Greasemonkey developers had the UserScripts.org site to distribute user scripts. Before becoming defunct, the site was troubled by DMCA requests from control-freak webmasters who did not quite understand user scripts, buckled under spam/DDOS attacks and went without a full-time admin. Many of the original developers from userscripts.org have not yet moved to the new sites. Hence, many user scripts are littered all over the web including sites such as gist.github.com. I would suggest ordinary readers to first trawl the comments section or the forums before installing any script or style. The Greasemonkey and Stylish extensions can be easily installed by doing a search in the Firefox add-on manager.

CSS Syntax

A CSS rule-set consists of a selector and a declaration block:

The selector points to the HTML element you want to style.

The declaration block contains one or more declarations separated by semicolons.

Each declaration includes a CSS property name and a value, separated by a colon.

Multiple CSS declarations are separated with semicolons, and declaration blocks are surrounded by curly braces.

In this example all <p> elements will be center-aligned, with a red text color:

p {   color: red;   text-align: center; }

  • is a selector in CSS (it points to the HTML element you want to style: <p>).
  • is a property, and is the property value
  • is a property, and is the property value

You will learn much more about CSS selectors and CSS properties in the next chapters.


JS Array concat() constructor copyWithin() entries() every() fill() filter() find() findIndex() forEach() from() includes() indexOf() isArray() join() keys() length lastIndexOf() map() pop() prototype push() reduce() reduceRight() reverse() shift() slice() some() sort() splice() toString() unshift() valueOf()

JS Boolean constructor prototype toString() valueOf()

JS Classes constructor() extends static super

JS Date constructor getDate() getDay() getFullYear() getHours() getMilliseconds() getMinutes() getMonth() getSeconds() getTime() getTimezoneOffset() getUTCDate() getUTCDay() getUTCFullYear() getUTCHours() getUTCMilliseconds() getUTCMinutes() getUTCMonth() getUTCSeconds() now() parse() prototype setDate() setFullYear() setHours() setMilliseconds() setMinutes() setMonth() setSeconds() setTime() setUTCDate() setUTCFullYear() setUTCHours() setUTCMilliseconds() setUTCMinutes() setUTCMonth() setUTCSeconds() toDateString() toISOString() toJSON() toLocaleDateString() toLocaleTimeString() toLocaleString() toString() toTimeString() toUTCString() UTC() valueOf()

JS Error name message

JS Global decodeURI() decodeURIComponent() encodeURI() encodeURIComponent() escape() eval() Infinity isFinite() isNaN() NaN Number() parseFloat() parseInt() String() undefined unescape()

JS JSON parse() stringify()

JS Math abs() acos() acosh() asin() asinh() atan() atan2() atanh() cbrt() ceil() cos() cosh() E exp() floor() LN2 LN10 log() LOG2E LOG10E max() min() PI pow() random() round() sin() sqrt() SQRT1_2 SQRT2 tan() tanh() trunc()

JS Number constructor isFinite() isInteger() isNaN() isSafeInteger() MAX_VALUE MIN_VALUE NEGATIVE_INFINITY NaN POSITIVE_INFINITY prototype toExponential() toFixed() toLocaleString() toPrecision() toString() valueOf()

JS OperatorsJS RegExp constructor compile() exec() g global i ignoreCase lastIndex m multiline n+ n* n? n{X} n{X,Y} n{X,} n$ ^n ?=n ?!n source test() toString() (x|y) . \w \W \d \D \s \S \b \B \0 \n \f \r \t \v \xxx \xdd \uxxxx

JS Statements break class continue debugger do…while for for…in for…of function if…else return switch throw try…catch var while

JS String charAt() charCodeAt() concat() constructor endsWith() fromCharCode() includes() indexOf() lastIndexOf() length localeCompare() match() prototype repeat() replace() search() slice() split() startsWith() substr() substring() toLocaleLowerCase() toLocaleUpperCase() toLowerCase() toString() toUpperCase() trim() valueOf()

JavaScript Exam — Get Your Diploma!

W3Schools’ Online Certification

The perfect solution for professionals who need to balance work, family, and career building.

More than 25 000 certificates already issued!

The HTML Certificate documents your knowledge of HTML.

The CSS Certificate documents your knowledge of advanced CSS.

The JavaScript Certificate documents your knowledge of JavaScript and HTML DOM.

The Python Certificate documents your knowledge of Python.

The jQuery Certificate documents your knowledge of jQuery.

The SQL Certificate documents your knowledge of SQL.

The PHP Certificate documents your knowledge of PHP and MySQL.

The XML Certificate documents your knowledge of XML, XML DOM and XSLT.

The Bootstrap Certificate documents your knowledge of the Bootstrap framework.

Class names

You may have noticed that the class names generated by our styling solution are non-deterministic, so you can’t rely on them to stay the same. The following CSS won’t work:

Instead, you have to use the property of a component to override them. On the other hand, thanks to the non-deterministic nature of our class names, we can implement optimizations for development and production. They are easy to debug in development and as short as possible in production:

  • development:
  • production:

If you don’t like this default behavior, you can change it. JSS relies on the concept of .

Global CSS

We provide a custom implementation of the class name generator for Material-UI needs: . As well as the option to make the class names deterministic with the option. When turned on, the class names will look like this:

  • development:
  • production:

️ Be cautious when using . We provide this option as an escape hatch for quick prototyping. Relying on it for code running in production has the following implications:

  • Global CSS is inherently fragile. People use strict methodologies like BEM to workaround the issue.
  • It’s harder to keep track of API changes.

️ When using standalone (without Material-UI), you should name your style sheets. has a name option for that:

User Style Examples

Here is a DuckDuckGo page. I use this search engine as the default because it has better respect for people. However, I found that the colors and the contrast on its web pages were not much to my liking. So, I wrote a User CSS for it, remembering to suffix the styles with a «!important» attribute to override the pages authors’ setting.

For the Wikipedia website, I use this CSS because the pages are usually text-heavy and take up the entire width of the screen. On big monitors, they can literally be a pain in the neck.

* { font-family: Century Schoolbook L!important; }
div#content { font-size: 1.2em; width: 7in;  }

Устранение неполадок при открытии файлов JSS

Общие проблемы с открытием файлов JSS

JSS (Javascript Style Sheets) не установлен

Дважды щелкнув по файлу JSS вы можете увидеть системное диалоговое окно, в котором сообщается «Не удается открыть этот тип файла». В этом случае обычно это связано с тем, что на вашем компьютере не установлено JSS (Javascript Style Sheets) для %%os%%. Так как ваша операционная система не знает, что делать с этим файлом, вы не сможете открыть его дважды щелкнув на него.

Совет: Если вам извстна другая программа, которая может открыть файл JSS, вы можете попробовать открыть данный файл, выбрав это приложение из списка возможных программ.

Установлена неправильная версия JSS (Javascript Style Sheets)

В некоторых случаях у вас может быть более новая (или более старая) версия файла JavaScript Style Sheet File, не поддерживаемая установленной версией приложения. При отсутствии правильной версии ПО JSS (Javascript Style Sheets) (или любой из других программ, перечисленных выше), может потребоваться загрузить другую версию ПО или одного из других прикладных программных средств, перечисленных выше. Такая проблема чаще всего возникает при работе в более старой версии прикладного программного средства с файлом, созданным в более новой версии, который старая версия не может распознать.

Совет: Иногда вы можете получить общее представление о версии файла JSS, щелкнув правой кнопкой мыши на файл, а затем выбрав «Свойства» (Windows) или «Получить информацию» (Mac OSX).

Резюме: В любом случае, большинство проблем, возникающих во время открытия файлов JSS, связаны с отсутствием на вашем компьютере установленного правильного прикладного программного средства.

Даже если на вашем компьютере уже установлено JSS (Javascript Style Sheets) или другое программное обеспечение, связанное с JSS, вы все равно можете столкнуться с проблемами во время открытия файлов JavaScript Style Sheet File. Если проблемы открытия файлов JSS до сих пор не устранены, возможно, причина кроется в других проблемах, не позволяющих открыть эти файлы. Такие проблемы включают (представлены в порядке от наиболее до наименее распространенных):

The typeof Operator

The typeof operator returns the type of a variable, object, function or expression:


typeof «John»                 // Returns string typeof 3.14                   // Returns number typeof NaN                    // Returns number typeof false                  // Returns boolean typeof            // Returns object typeof {name:’John’, age:34}  // Returns objecttypeof new Date()             // Returns objecttypeof function () {}         // Returns function typeof myCar                  // Returns undefined (if myCar is not declared) typeof null                   // Returns object

Please observe:

  • The data type of NaN is number
  • The data type of an array is object
  • The data type of a date is object
  • The data type of null is object
  • The data type of an undefined variable is undefined

You cannot use typeof to define if a JavaScript object is an array (or a date).

JavaScript Arithmetic Operators

Arithmetic operators are used to perform arithmetic between variables and/or values.

Given that y = 5, the table below explains the arithmetic operators:

Operator Description Example Result in y Result in x Try it
+ Addition x = y + 2 y = 5 x = 7 Try it »
Subtraction x = y — 2 y = 5 x = 3 Try it »
* Multiplication x = y * 2 y = 5 x = 10 Try it »
Division x = y / 2 y = 5 x = 2.5 Try it »
% Modulus (division remainder) x = y % 2 y = 5 x = 1 Try it »
++ Increment x = ++y y = 6 x = 6 Try it »
x = y++ y = 6 x = 5 Try it »
Decrement x = —y y = 4 x = 4 Try it »
x = y— y = 4 x = 5 Try it »

For a tutorial about arithmetic operators, read our JavaScript Arithmetic Tutorial.

Using Javascript to Build Web Applications

In this module, we are going to take all those newly learned Javascript language skills and learn how to utilize them within the context of a web page. We’ll start by learning how to properly manipulate the web page components using the Javascript Document Object Model API. We will then move on to learning one of the most popular ways of serving up data to a web site — Ajax. We’ll learn about the protocol that the language of the web speaks in (HTTP), how to set up and handle Ajax requests and responses, as well as how to process JSON data. We’ll finish the module by connecting our restaurant web site from Module 3 to a real backend service that will allow us to pull the data for the restaurant menu dynamically from the server without having to reload the entire page.

Hours to complete 5 hours to complete

Reading 17 videos (Total 137 min), 6 readings, 4 quizzes

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What can JavaScript Do?

Event handlers can be used to handle, and verify, user input, user actions, and browser actions:

  • Things that should be done every time a page loads
  • Things that should be done when the page is closed
  • Action that should be performed when a user clicks a button
  • Content that should be verified when a user inputs data
  • And more …

Many different methods can be used to let JavaScript work with events:

  • HTML event attributes can execute JavaScript code directly
  • HTML event attributes can call JavaScript functions
  • You can assign your own event handler functions to HTML elements
  • You can prevent events from being sent or being handled
  • And more …

You will learn a lot more about events and event handlers in the HTML DOM chapters.

Introduction to Javascript

What fun would a web site be if there was no functionality to it? In this module, we are going to concentrate on learning the fundamentals of the Javascript language. A lot of even seasoned developers “tinker” with Javascript without really understanding how the language works. That leads to viewing the language as more of a nuisance instead of a powerful tool. That is why we are going to concentrate not only on the “how” but also on the “why”, so you are empowered by the Javascript language features, not confused by them. We’ll cover just about everything — from common language constructs and Javascript types to objects, functions, arrays, closures, and scope isolation.

Hours to complete 5 hours to complete

Reading 24 videos (Total 151 min), 3 readings, 10 quizzes

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HTML Events

An HTML event can be something the browser does, or something a user does.

Here are some examples of HTML events:

  • An HTML web page has finished loading
  • An HTML input field was changed
  • An HTML button was clicked

Often, when events happen, you may want to do something.

JavaScript lets you execute code when events are detected.

HTML allows event handler attributes, with JavaScript code, to be added to HTML elements.

With single quotes:

<element event=’some JavaScript’>

With double quotes:

<element event=»some JavaScript»>

In the following example, an attribute (with code), is added to a element:

<button onclick=»document.getElementById(‘demo’).innerHTML = Date()»>The time is?</button>

In the example above, the JavaScript code changes the content of the element with id=»demo».

In the next example, the code changes the content of its own element (using ):

<button onclick=»this.innerHTML = Date()»>The time is?</button>

JavaScript code is often several lines long. It is more common to see event attributes calling functions:

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