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Introduction to webtechnologiesHTML + CSS + JavascriptJavi Agenjo (@tamat)

GoalsIntroduction to web technologies:● HTML to create the documentstructure and content● CSS to control is visual aspect● Javascript for interactivity

DeployWhat do we need to start:- a good web-browser (Chrome or Firefox)- the example HTML code to start- a good text editor like Editplus (win), VSCode (cross platform),textWrangler (osx), vim (unix) or sublime text (cross platform)

How can I test my codeJust open the index.html from the template in your text editor and in yourbrowser.When you do any change to the code, check it in the browser by pressingF5 (refresh site)To open the developer tools press:Windows: Control + Shift + I or F12OSX: Command + Opt + IOther tools are online editors like scratchpad or htmledit

Inside a browserBrowsers have very differentiateparts.We are interested in two of them:● the Rendering Engine (incharge of transforming ourHTML+CSS in a visualimage).● The Javascript Interpreter(also known as VM), incharge of executing theJavascript code.

Technologies● HTML● CSS● Javascript

HTMLHTML means Hyper Text Markup Language.The HTML allow us to define the structure of a document or awebsite.HTML is NOT a programming language, it’s a markup language,which means its purpose is to give structure to the content of thewebsite, not to define an algorithm.It is a series of nested tags (it is a subset of XML) that contain allthe website information (like texts, images and videos). Here is anexample of tags:<title>This is a title</title>The HTML defines the page structure. A website can have severalHTMLs to different pages.<html><head></head><body><div><p>Hi</p></div></body></html>

HTML: basic rulesSome rules about HTML:● It uses XML syntax (tags with attributes, can contain other tags).<tag_name attribute="value"> content </tag_name>● It stores all the information that must be shown to the user.● There are different HTML elements for different types of information and behaviour.● The information is stored in a tree-like structure (nodes that contain nodes inside) calledDOM (Document Object Model).● It gives the document some semantic structure (pe. this is a title, this is a section, this isa form) which is helpful for computers to understand websites content.● It must not contain information related to how it should be displayed (that informationbelongs to the CSS), so no color information, font size, position, etc.

HTML: syntax example<div id="main">This is text without a tag.<button class="mini">press me</button><img src="me.png" /></div>

HTML: syntax example<div id="main">This is text without a tag.<button class="mini">press me</button><img src="me.png" /></div>Tag nameattributescommenttext tagself-closing tag

DOM is a treeEvery node can only haveone parent, and every nodecan have several children,so the structure looks like atree.

Although there are lots of tags in the HTML specification, 99% of the webs use a subset ofHTML tags with less that 10 tags, the most important are:● <div>: a container, usually represents a rectangular area with information inside.● <img/>: an image● <a>: a clickable link to go to another URL● <p>: a text paragraph● <h1>: a title (h2,h3,h4 are titles of less importance)● <input>: a widget to let the user introduce information● <style>: to insert CSS rules● <script>: to execute Javascript● <span>: a null tag (doesn't do anything)HTML: main tags

HTML: other interesting tagsThere are some tags that could be useful sometimes:● <button>: to create a button● <audio>: for playing audio● <video>: to play video● <canvas>: to draw graphics from javascript● <iframe>: to put another website inside ours

HTML: wrapping the infoWe use HTML tags to wrap differentinformation on our site.The more structure has the information, theeasier will be to access it and present it.We can change the way the information isrepresented on the screen depending on thetags where it is contained, so we shouldn't beworried about using too many tags.

HTML: tagging correctlyTry to avoid doing this:<div>TitleHere is some contentHere is more content</div>Do this instead<div><h1>Title</h1><p>Here is content.</p><p>Here is more content</p></div>DONT DO THIS

HTML good useIt is good to have all the information properly wrapped in tags that give it some semantics.We also can extend the code semantics by adding extra attributes to the tags:● id: tells a unique identifier for this tag● class: tells a generic identifier for this tag<div id="profile-picture" class="mini-image">...</div>

HTML referencesHTML Reference: a description of all HTML tags.The 25 Most used tags: a list with information of the morecommon tags.HTML5 Good practices: some tips for starters

CSSCSS allows us to specify how to present(render) the document info stored in theHTML.Thanks to CSS we can control all theaspects of the visualization and some otherfeatures:● Colors: content, background, borders● Margins: interior margin, exteriormargin● Position: where to put it● Sizes: width, height● Behaviour: changes on mouse over

CSS example* {color: blue; /*a comment */margin: 10px;font: 14px Tahoma;}This will change all the tags in my web ( ‘*‘ means all) to look blue with font Tahoma with14px, and leaving a margin of 10px around.

CSS fieldsHere is a list of the most common CSS fields and an example:● color: #FF0000; red; rgba(255,00,100,1.0); //different ways to specify colors● background-color: red;● background-image: url('file.png');● font: 18px 'Tahoma';● border: 2px solid black;● border-top: 2px solid red;● border-radius: 2px; //to remove corners and make them more round● margin: 10px; //distance from the border to the outer elements● padding: 2px; //distance from the border to the inner elements● width: 100%; 300px; 1.3em; //many different ways to specify distances● height: 200px;● text-align: center;● box-shadow: 3px 3px 5px black;● cursor: pointer;● display: inline-block;● overflow: hidden;

CSS how to add itThere are four ways to add CSS rules to your website:● Inserting the code inside a style tag<style>p { color: blue }</style>● Referencing an external CSS file<link href="style.css" rel="stylesheet" />● Using the attribute style on a tag<p style="color: blue; margin: 10px">● Using Javascript (we will see this one later).

CSS selectorsLet's start by changing the background color of one tag of our website:div {background-color: red;}This CSS rule means that every tag DIV found in our website should have a red backgroundcolor. Remember that DIVs are used mostly to represent areas of our website.We could also change the whole website background by affecting the tag body:body {background-color: red;}

CSS selectorsWhat if we want to change one specific tag (not all the tags of the same type).We can specify more precise selectors besides the name of the tag. For instance, by classor id. To specify a tag with a given class name, we use the dot:p.intro {color: red;}This will affect only the tags p with class name intro:<p class="intro">

CSS SelectorsThere are several selectors we can use to narrow our rules to very specific tags of our website.The main selectors are:● tag name: just the name of the tag○ p { ... } //affects to all <p> tags● dot (.): affects to tags with that class○ p.highlight { ... } //affects all <p> tags with class="highlight"● sharp character (#): specifies tags with that id○ p#intro { ... } //affects to the <p> tag with the id="intro"● two dots (:): behaviour states (mouse on top)○ p:hover { ... } //affects to <p> tags with the mouse over● brackets ([attr='value']): tags with the attribute attr with the value 'value'○ input[type="text"] {...} // affects to the input tags of the type text

CSS SelectorsYou can also specify tags by its context, for example: tags that are inside of tags matching aselector. Just separate the selectors by an space:div#main p.intro { ... }This will affect to the p tags of class intro that are inside the tag div of id main<div id="main"><p class="intro">....</p> ← Affects this one</div><p class="intro">....</p> ← but not this one

CSS SelectorsAnd you can combine selectors to narrow it down more.div#main.intro:hover { ... }will apply the CSS to the any tag div with id main and class intro if the mouse is over.And you do not need to specify a tag, you can use the class or id selectors without tag, thismeans it will affect to any node of id main#main { ... }

CSS SelectorsIf you want to select only elements that are direct child of one element (not that have anancestor with that rule), use the > character:ul.menu > li { ... }Finally, if you want to use the same CSS actions to several selectors, you can use thecomma , character:div, p { … } ← this will apply to all divs and p tags

HTML arrangeIt is important to understand how the browserarranges the elements on the screen.Check this tutorial where it explains thedifferent ways an element can be arrangedon the screen.You can change the way elements arearranged using the display property:div { display: inline-block; }Also check the property float.

Box ModelIt is important to note that by default anywidth and height specified to an element willnot take into account its margin, so a div withwidth 100px and margin 10px will measure120px on the screen, not 100px.This could be a problem breaking yourlayout.You can change this behaviour changing thebox model of the element so the width usesthe outmost border:div { box-sizing: border; }

LayoutOne of the hardest parts of CSS isconstruing the layout of your website (thestructure inside the window) .By default HTML tends to put everything inone column, which is not ideal.There has been many proposals in CSS toaddress this issue (tables, fixed divs, flex,grid, …).

Grid systemBecause most sites are structured in a grid, Irecommend to use the CSS Grid system.Check this tutorial to create the site structureeasilyHTML<div class="grid-container"><div class="grid-item1">1</div><div class="grid-item2">2</div></div>CSS.grid-container {display: grid;grid-template-rows: 100px; 100px;grid-template-columns: 100px; 100px; 100px;grid-gap: 5px;}.grid-item1 {background: blue;border: black 5px solid;grid-column-start: 1;grid-column-end: 5;grid-row-start: 1;grid-row-end: 3;}

Fullscreen divsSometimes we want to have a div that coversthe whole screen (to make a webapp),instead of a scrolling website (more likeregular documents).In that case remember to use percentages todefine the size of elements, but keep in mindthat percentages are relative to the element'sparent size, so you must set the size to the<body> element to use 100%.CSShtml, body {width: 100%;height: 100%;}div {margin: 0;padding: 0;}#main {width: 100%;height: 100%;}

Trick to center.horizontal-and-vertical-centering {display: flex;justify-content: center;align-items: center;}Centering divs can be hard sometimes, use this trick:

CSS further readingThere are many more rules for selectors.Check some of the links to understand them better.One line layouts tutorialsUnderstanding the Box Model: a good explanation of how to position the information on yourdocument.All CSS Selectors: the CSS selectors specification page.CSS Transition: how to make animations just using CSS

JavascriptA regular programming language, easy to start, hard to master.Allows to give some interactivity to the elements on the web.Syntax similar to C or Java but with no types.You can change the content of the HTML or the CSS applied to an element.You can even send or retrieve information from the internet to update the contentof the web without reloading the page.

Javascript example<html><body><h1>This is a title</h1><script>var title = document.querySelector("h1");title.innerHTML = "This is another title";</script></body></html>

Javascript APIJavascript comes with a rich API to do many things like:● Access the DOM (HTML nodes)● Do HTTP Requests● Play videos and sounds● Detect user actions (mouse move, key pressed)● Launch Threads● Access the GPU, get the Webcam image, ...And the API keeps growing with every new update of the standard.Check the WEB API reference to know more

Using InputsIf you want the user to be able to input some text we use the tag <input>:<input type="text"/>There are other inputs, you can check this list.From Javascript we can attach events like "click" or "keydown".To read or modify the content of the input:my_input_element.value = ""; //this will clear the text inside the input

Example of a websiteHTML in index.html<link href="style.css" rel="stylesheet"/><h1>Welcome</h1><p><button>Click me</button></p><script src=”code.js”/>CSS in style.cssh1 { color: #333; }button {border: 2px solid #AAA;background-color: #555;}Javascript in code.js//fetch the button from the DOMvar button = document.querySelector(“button”);//attach and event when the user clicks itbutton.addEventListener(“click”, myfunction);//create the function that will be called when thebutton is pressedfunction myfunction(){//this shows a popup windowalert(“button clicked!”);}

jQueryjQuery is a library that makes working with the DOM much easier, using an unifiedsyntax and taking advantage of selectors:$("p").remove(); //remove all tags p$("#main").hide(); //hides the element of id main$("#main").append("<h1>titulo</h1>") //adds content to an element$("#wrap").css({ color: "red" }); //change the css$("button#send").click( function() { /* code */ });To include this library just add this to your HTML:<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.4.1/jquery.min.js"></script>

Using the Dev ToolsPress Control + Shift + I (or F12) to open DevTools

ExerciseCreate the layout for amessaging application.Structured like:● Main container○ Messages area■ message○ Typing area area■ input

Further infoAPI References: DevDocs.ioSelectors: MDN TutorialTo learn Javascript.http://codeacademy.comTo learn jQuery:http://docs.jquery.com/Tutorials

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