Neste artigo nós iremos abranger os básicos absolutos de HTML, para o iniciar — nós definimos os elementos, atributos, e todos os outros termos importantes que já poderá ter ouvido, e onde os incorporar na linguagem. Nós também mostramos como é que o elemento de HTML é estruturado, como é que uma página HTML é estruturada, e explicar outras funcionalidades de linguagem básica importantes. E nós iremos algumas demonstrações de algum HTML, para o motivar!
| Pré-requisitos: | Basic computer literacy, basic software installed, and basic knowledge of working with files. |
|---|---|
| Objetivo: | To gain basic familiarity with the HTML language, and get some practice writing a few HTML elements. |
{{glossary("HTML")}} (Linguagem de Marcação de Hipertexto) não é uma linguagem de programação; é uma linguagem de marcação utilizada para comunicar ao seu navegador como estruturar as páginas da Web que visita. Este pode ser tão complicado ou tão simples como o programador da Web o desejar. HTML consiste em uma série de {{glossary("Element", "elementos")}}, que utiliza para incluir, ou marcar diferentes partes do conteúdo para que este apareça ou atue de uma determinada maneira. A inclusão de {{glossary("Tag", "etiquetas")}} pode tornar uma parte do conteúdo em uma hiperligação para interligar com outra página na Web, colocar as palavras em itálico, e assim por diante. Por exemplo, siga a seguinte linha de conteúdo:
My cat is very grumpy
Se quisermos que a linha esteja demarcada, podemos especificar que é um parágrafo, encerrando-a num elemento com tag de parágrafo ({{htmlelement("p")}}) :
<p>My cat is very grumpy</p>
Vamos explorar o nosso elemento parágrafo um pouco mais:
As partes principais do nosso elemento são:
Edit the line below in the Input area by wrapping it with the tags <em> and </em> (put <em> before it to open the element, and </em> after it, to close the element) — this should give the line italic emphasis! You'll be able to see your changes update live in the Output area.
If you make a mistake, you can always reset it using the Reset button. If you get really stuck, press the Show solution button to see the answer.
<h2>Input</h2> <textarea id="code" class="input">This is my text.</textarea> <h2>Output</h2> <div class="output"></div> <div class="controls"> <input id="reset" type="button" value="Reset" /> <input id="solution" type="button" value="Show solution" /> </div>
body {
font-family: 'Open Sans Light',Helvetica,Arial,sans-serif;
}
.input, .output {
width: 90%;
height: 2em;
padding: 10px;
border: 1px solid #0095dd;
}
button {
padding: 10px 10px 10px 0;
}
var textarea = document.getElementById("code");
var reset = document.getElementById("reset");
var code = textarea.value;
var output = document.querySelector(".output");
var solution = document.getElementById("solution");
function drawOutput() {
output.innerHTML = textarea.value;
}
reset.addEventListener("click", function() {
textarea.value = code;
drawOutput();
});
solution.addEventListener("click", function() {
textarea.value = '<em>This is my text.</em>';
drawOutput();
});
textarea.addEventListener("input", drawOutput);
window.addEventListener("load", drawOutput);
{{ EmbedLiveSample('Playable_code', 700, 300) }}
You can put elements inside other elements too — this is called nesting. If we wanted to state that our cat is very grumpy, we could wrap the word "very" in a {{htmlelement("strong")}} element, which means that the word is to be strongly emphasized:
<p>My cat is <strong>very</strong> grumpy.</p>
You do however need to make sure that your elements are properly nested: in the example above we opened the p element first, then the strong element, therefore we have to close the strong element first, then the p. The following is incorrect:
<p>My cat is <strong>very grumpy.</p></strong>
The elements have to open and close correctly so they are clearly inside or outside one another. If they overlap like above, then your web browser will try to make a best guess at what you were trying to say, and you may well get unexpected results. So don't do it!
There are two important categories of elements in HTML, which you should know about — block-level elements and inline elements.
Take the following example:
<em>first</em><em>second</em><em>third</em> <p>fourth</p><p>fifth</p><p>sixth</p>
{{htmlelement("em")}} is an inline element, so as you can see below, the first three elements sit on the same line as one another with no space in between. On the other hand, {{htmlelement("p")}} is a block-level element, so each element appears on a new line, with space above and below each (the spacing is due to default CSS styling that the browser applies to paragraphs).
{{ EmbedLiveSample('Block_versus_inline_elements', 700, 200) }}
Nota: HTML5 redefined the element categories in HTML5: see Element content categories. While these definitions are more accurate and less ambiguous than the ones that went before, they are a lot more complicated to understand than "block" and "inline", so we will stick with these throughout this topic.
Nota: You can find useful reference pages that include lists of block and inline elements — see Block-level elements and Inline elements.
Not all elements follow the above pattern of opening tag, content, closing tag. Some elements consist only of a single tag, which is usually used to insert/embed something in the document at the place it is included. For example, the {{htmlelement("img")}} element embeds an image file onto a page in the position it is included in:
<img src="https://raw.githubusercontent.com/mdn/beginner-html-site/gh-pages/images/firefox-icon.png">
This would output the following on your page:
{{ EmbedLiveSample('Empty_elements', 700, 300) }}
Nota: Empty elements are also sometimes called void elements.
Elements can also have attributes, which look like this:
Attributes contain extra information about the element which you don't want to appear in the actual content. In this case, the class attribute allows you to give the element an identifying name that can be later used to target the element with style information and other things.
An attribute should have:
Another example of an element is {{htmlelement("a")}} — this stands for anchor and will make the piece of text it wraps around into a hyperlink. This can take a number of attributes, but several are as follows:
href: This attribute specifies as its value the web address that you want the link to point to; where the browser navigates to when the link is clicked. For example, href="https://www.mozilla.org/".title: The title attribute specifies extra information about the link, such as what the page is that you are linking to. For example, title="The Mozilla homepage". This will appear as a tooltip when hovered over.target: The target attribute specifies the browsing context which will be used to display the link. For example, target="_blank" will display the link in a new tab. If you want to display the link in the current tab just omit this attribute.Edit the line below in the Input area to turn it into a link to your favourite website. First, add the <a> element. Second, add the href attribute and the title attribute. Lastly, specify target attribute to open the link in the new tab. You'll be able to see your changes update live in the Output area. You should see a link that when hovered over displays the title attribute's content, and when clicked navigates to the web address in the href element. Remember that you need to include a space between the element name, and each attribute.
If you make a mistake, you can always reset it using the Reset button. If you get really stuck, press the Show solution button to see the answer.
<h2>Input</h2> <textarea id="code" class="input"><p>A link to my favourite website.</p></textarea> <h2>Output</h2> <div class="output"></div> <div class="controls"> <input id="reset" type="button" value="Reset" /> <input id="solution" type="button" value="Show solution" /> </div>
body {
font-family: 'Open Sans Light',Helvetica,Arial,sans-serif;
}
.input, .output {
width: 90%;
height: 2em;
padding: 10px;
border: 1px solid #0095dd;
}
button {
padding: 10px 10px 10px 0;
}
var textarea = document.getElementById("code");
var reset = document.getElementById("reset");
var code = textarea.value;
var output = document.querySelector(".output");
var solution = document.getElementById("solution");
function drawOutput() {
output.innerHTML = textarea.value;
}
reset.addEventListener("click", function() {
textarea.value = code;
drawOutput();
});
solution.addEventListener("click", function() {
textarea.value = '<p>A link to my <a href="https://www.mozilla.org/" title="The Mozilla homepage" target="_blank">favourite website</a>.</p>';
drawOutput();
});
textarea.addEventListener("input", drawOutput);
window.addEventListener("load", drawOutput);
{{ EmbedLiveSample('Playable_code2', 700, 300) }}
You'll sometimes see attributes written without values — this is perfectly allowed. These are called boolean attributes, and they can only have one value, which is generally the same as the attribute name. As an example, take the {{htmlattrxref("disabled", "input")}} attribute, which you can assign to form input elements if you want them to be disabled (greyed out) so the user can't enter any data in them.
<input type="text" disabled="disabled">
As shorthand, it is perfectly allowable to write this as follows (we've also included a non-disabled form input element for reference, to give you more of an idea what is going on):
<input type="text" disabled> <input type="text">
Both will give you an output as follows:
{{ EmbedLiveSample('Boolean_attributes', 700, 100) }}
When you look around the World Wide Web, you'll come across all kind of strange markup styles, including attribute values without quotes. This is allowable in certain circumstances, but will break your markup in others. For example, if we revisit our link example from earlier, we could write a basic version with only the href attribute, like this:
<a href=https://www.mozilla.org/>favourite website</a>
However, as soon as we add the title attribute in this style, things will go wrong:
<a href=https://www.mozilla.org/ title=The Mozilla homepage>favourite website</a>
At this point the browser will misinterpret your markup, thinking that the title attribute is actually three attributes — a title attribute with the value "The", and two boolean attributes, Mozilla and homepage. This is obviously not what was intended, and will cause errors or unexpected behaviour in the code, as seen in the live example below. Try hovering over the link to see what the title text is!
{{ EmbedLiveSample('Omitting_quotes_around_attribute_values', 700, 100) }}
Our advice is to always include the attribute quotes — it avoids such problems, and results in more readable code too.
In this article you'll notice that the attributes are all wrapped in double quotes. You might however see single quotes in some people's HTML. This is purely a matter of style, and you can feel free to choose which one you prefer. Both the following lines are equivalent:
<a href="http://www.example.com">A link to my example.</a> <a href='http://www.example.com'>A link to my example.</a>
You should however make sure you don't mix them together. The following will go wrong!
<a href="http://www.example.com'>A link to my example.</a>
If you've used one type of quote in your HTML, you can include the other type of quote without causing any problems:
<a href="http://www.example.com" title="Isn't this fun?">A link to my example.</a>
However if you want to include a quote within the quotes where both the quotes are of the same type(single quote or double quote), you'll have to use HTML entities for the quotes.
That wraps up the basics of individual HTML elements, but they aren't very useful on their own. Now we'll look at how individual elements are combined to form an entire HTML page:
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>My test page</title>
</head>
<body>
<p>This is my page</p>
</body>
</html>
Here we have:
<!DOCTYPE html>: The doctype. In the mists of time, when HTML was young (about 1991/2), doctypes were meant to act as links to a set of rules that the HTML page had to follow to be considered good HTML, which could mean automatic error checking and other useful things. They used to look something like this:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">However, these days no one really cares about them, and they are really just a historical artifact that needs to be included for everything to work right.
<!DOCTYPE html> is the shortest string of characters that counts as a valid doctype; that's all you really need to know.<html></html>: The {{htmlelement("html")}} element. This element wraps all the content on the entire page, and is sometimes known as the root element.<head></head>: The {{htmlelement("head")}} element. This element acts as a container for all the stuff you want to include on the HTML page that isn't the content you are showing to your page's viewers. This includes things like keywords and a page description that you want to appear in search results, CSS to style our content, character set declarations, and more. You'll learn more about this in the next article in the series.<meta charset="utf-8">: This element sets the character set your document should use to UTF-8, which includes most characters from the vast majority of human written languages. Essentially it can now handle any textual content you might put on it. There is no reason not to set this, and it can help avoid some problems later on.<title></title>: The {{htmlelement("title")}} element. This sets the title of your page, which is the title that appears in the browser tab the page is loaded in, and is used to describe the page when you bookmark/favourite it.<body></body>: The {{htmlelement("body")}} element. This contains all the content that you want to show to web users when they visit your page, whether that's text, images, videos, games, playable audio tracks, or whatever else.If you want to experiment with writing some HTML on your local computer, you can:
index.html.Nota: You can also find this basic HTML template on the MDN Learning Area Github repo.
You can now open this file in a web browser to see what the rendered code looks like, and then edit the code and refresh the browser to see what the result is. Initially it will look like this:
So in this exercise, you can edit the code locally on your computer, as outlined above, or you can edit it in the editable sample window below (the editable sample window represents just the contents of the {{htmlelement("body")}} element, in this case.) We'd like you to have a go at implementing the following steps:
<h1> opening tag and </h1> closing tag.<strong> opening tag and </strong> closing tagIf you make a mistake, you can always reset it using the Reset button. If you get really stuck, press the Show solution button to see the answer.
<h2>Input</h2> <textarea id="code" class="input"> <p>This is my page</p></textarea> <h2>Output</h2> <div class="output"></div> <div class="controls"> <input id="reset" type="button" value="Reset" /> <input id="solution" type="button" value="Show solution" /> </div>
body {
font-family: 'Open Sans Light',Helvetica,Arial,sans-serif;
}
.input, .output {
width: 90%;
height: 10em;
padding: 10px;
border: 1px solid #0095dd;
}
img {
max-width: 100%;
}
.output {
overflow: auto;
}
button {
padding: 10px 10px 10px 0;
}
var textarea = document.getElementById("code");
var reset = document.getElementById("reset");
var code = textarea.value;
var output = document.querySelector(".output");
var solution = document.getElementById("solution");
function drawOutput() {
output.innerHTML = textarea.value;
}
reset.addEventListener("click", function() {
textarea.value = code;
drawOutput();
});
solution.addEventListener("click", function() {
textarea.value = '<p>I really enjoy <strong>playing the drums</strong>. One of my favourite drummers is Neal Peart, who\
plays in the band <a href="https://en.wikipedia.org/wiki/Rush_%28band%29" title="Rush Wikipedia article">Rush</a>.\
My favourite Rush album is currently <a href="http://www.deezer.com/album/942295">Moving Pictures</a>.</p>\
<img src="http://www.cygnus-x1.net/links/rush/images/albums/sectors/sector2-movingpictures-cover-s.jpg">';
drawOutput();
});
textarea.addEventListener("input", drawOutput);
window.addEventListener("load", drawOutput);
{{ EmbedLiveSample('Playable_code3', 700, 600) }}
In the above examples you may have noticed that a lot of whitespace is included in the code listings — this is not necessary at all; the two following code snippets are equivalent:
<p>Dogs are silly.</p>
<p>Dogs are
silly.</p>
No matter how much whitespace you use (which can include space characters, but also line breaks), the HTML parser reduces each one down to a single space when rendering the code. So why use so much whitespace? The answer is readability — it is so much easier to understand what is going on in your code if you have it nicely formatted, and not just bunched up together in a big mess. In our HTML we've got each nested element indented by two spaces more than the one it is sitting inside. It is up to you what style of formatting you use (how many spaces for each level of indentation, for example), but you should consider using some kind of formatting.
In HTML, the characters <, >,",' and & are special characters. They are parts of the HTML syntax itself, so how do you include one of these characters in your text, for example if you really want to use an ampersand or less than sign, and not have it interpreted as code as some browsers may do?
We have to use character references — special codes that represent characters, and can be used in these exact circumstances. Each character reference is started with an ampersand (&), and ended by a semi-colon (;).
| Caráter literal | Referência de caráter equivalente |
|---|---|
| < | < |
| > | > |
| " | " |
| ' | ' |
| & | & |
In the below example, you can see two paragraphs, which are talking about web technologies:
<p>In HTML, you define a paragraph using the <p> element.</p> <p>In HTML, you define a paragraph using the <p> element.</p>
In the live output below, you can see that the first paragraph has gone wrong, because the browser thinks that the second instance of <p> is starting a new paragraph. The second paragraph looks fine, because we have replaced the angle brackets with character references.
{{ EmbedLiveSample('Entity_references_including_special_characters_in_HTML', 700, 200) }}
Nota: A chart of all the available HTML character entity references can be found on Wikipedia: List of XML and HTML character entity references.
In HTML, as with most programming languages, there is a mechanism available to write comments in the code — comments are ignored by the browser and invisible to the user, and their purpose is to allow you to include comments in the code to say how your code works, what the different parts of the code do, etc. This can be very useful if you return to a code base that you've not worked on for six months, and can't remember what you did — or if you hand your code over to someone else to work on.
To turn a section of content inside your HTML file into a comment, you need to wrap it in the special markers <!-- and -->, for example:
<p>I'm not inside a comment</p> <!-- <p>I am!</p> -->
As you can see below, the first paragraph appears in the live output, but the second one doesn't.
{{ EmbedLiveSample('HTML_comments', 700, 100) }}
You've reached the end of the article — we hope you enjoyed your tour of the very basics of HTML! At this point you should understand what the language looks like, how it works at a basic level, and be able to write a few elements and attributes. This is a perfect place to be right now, as in subsequent articles in the module we will go into some of the things you have already looked at in a lot more detail, and introduce some new features of the language. Stay tuned!
Note: At this point, as you start to learn more about HTML, you might also want to start to explore the basics of Cascading Style Sheets, or CSS. CSS is the language you use to style your web pages (whether e.g. changing the font or colors, or altering the page layout). HTML and CSS go very well together, as you'll soon discover.