Document Object Model DOM

Intro

DOM is the interface between Javascript and HTML+CSS. The browser turns every HTML tag into a Javascript object that we can manipulate. Everything is stored inside the document object.

Select and manipulate

var h1 = document.querySelector("h1");
h1.style.color = "pink";

Select

document.getElementById()
document.getElementsByClassName()
document.getElementsByTagName()
document.querySelector()
- returns the first element that matches a given CSS-style selector
- document.querySelector("#highlight")
document.querySelectorAll()
- return all matching elements

Manipulate

changing an element’s style
adding/removing classes
changing the content of a tag
changing attributes(src, href, etc.)

Style

var tag = document.getElementById(highlight);

// manipulate
tag.style.color = "blue";
tag.style.border = "10px solid red";

It’s recommended for styles to be defined in a separated file or files. So just use js to turn on or off, switch between styles.

.some-class {
    color: blue;
    border: 10px solid red;
}

var tag = document.getElementById(highlight);
// add the css class
tag.classList.add("some-class");

//remove
tag.classList.remove("another-class");

//toggle
    // if the tag has the class name, remove it
    // else, turn it on
tag.classList.toggle("another-class");

Text and content

textContent will return a string of all the text contained in a given element.
innerHTML is similar, but it returns a string of all HTML contained in a given element.

<p> This is a <strong>good</strong> para</p>

var tag = document.querySelector("p");

// Retrieve the text
tag.textContent; // This is a good para
tag.innerHTML; // This is a <strong>good</strong> para

// alter
tag.textContent = "new";
tag.innerHTML = "<strong>goodbye</strong>";

Attributes

Use getAttribute() and setAttribute() to read and write attributes like src or href.

<a href="www.google.com">link</a>
<img src="logo.png">

var link = document.querySelector("a");
link.getAttribute("href");
link.setAttribute("href", "http://www.facebook.com");

Events

Click on a button
Hovering over a link
Dragging and dropping
Pressing the enter key

Process is that we select an element and then add an event listener. Multiple listeners can be added.

List of events ref: https://developer.mozilla.org/en-US/docs/Web/Events

element.addEventListener(type, functionToCall);

// example
var button = document.querySelector("button");
button.addEventListener("click", function() {
    console.log("CLICKED");
});

Example events

mouseover: the moment that mouse starts being on the element
mouseout: the moment that mouse leaves the element
input: the value of input tag changes

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