JavaScript – Page 4 – Iampsp Blog

Since modern browsers have implemented (almost) the same methods and properties for JavaScript interactivity, it is often referred to, as methods and properties of the BOM. Continue reading JavaScript Window

JavaScript HTML DOM Node Lists

The HTML DOM NodeList Object

A NodeList object is a list (collection) of nodes extracted from a document.

A NodeList object is almost the same as an HTMLCollection object.

Some (older) browsers return a NodeList object instead of an HTMLCollection for methods like getElementsByClassName().

All browsers return a NodeList object for the property childNodes.

Most browsers return a NodeList object for the method querySelectorAll(). Continue reading JavaScript HTML DOM Node Lists

JavaScript HTML DOM Collections

The HTMLCollection Object

The getElementsByTagName() method returns an HTMLCollection object.

An HTMLCollection object is an array-like list (collection) of HTML elements.

The following code selects all <p> elements in a document:

Example

const myCollection = document.getElementsByTagName("p");

The elements in the collection can be accessed by an index number.

To access the second <p> element you can write:

myCollection[1]

Continue reading JavaScript HTML DOM Collections

JavaScript HTML DOM Elements (Nodes)

Adding and Removing Nodes (HTML Elements)

Creating New HTML Elements (Nodes)

To add a new element to the HTML DOM, you must create the element (element node) first, and then append it to an existing element.

Example

<div id="div1">
  <p id="p1">This is a paragraph.</p>
  <p id="p2">This is another paragraph.</p>
</div>

<script>
const para = document.createElement("p");
const node = document.createTextNode("This is new.");
para.appendChild(node);

const element = document.getElementById("div1");
element.appendChild(para);
</script>

Example Explained

This code creates a new <p> element:

const para = document.createElement("p");

To add text to the <p> element, you must create a text node first. This code creates a text node : Continue reading JavaScript HTML DOM Elements (Nodes)

JavaScript HTML DOM Navigation

With the HTML DOM, you can navigate the node tree using node relationships.

DOM Nodes

According to the W3C HTML DOM standard, everything in an HTML document is a node:

The entire document is a document node
Every HTML element is an element node
The text inside HTML elements are text nodes
Every HTML attribute is an attribute node (deprecated)
All comments are comment nodes

With the HTML DOM, all nodes in the node tree can be accessed by JavaScript.

New nodes can be created, and all nodes can be modified or deleted. Continue reading JavaScript HTML DOM Navigation

JavaScript HTML DOM EventListener

The addEventListener() method

Example

Add an event listener that fires when a user clicks a button:

document.getElementById("myBtn").addEventListener("click", displayDate);

The addEventListener() method attaches an event handler to the specified element.

The addEventListener() method attaches an event handler to an element without overwriting existing event handlers.

You can add many event handlers to one element.

You can add many event handlers of the same type to one element, i.e two “click” events.

You can add event listeners to any DOM object not only HTML elements. i.e the window object.

The addEventListener() method makes it easier to control how the event reacts to bubbling.

When using the addEventListener() method, the JavaScript is separated from the HTML markup, for better readability and allows you to add event listeners even when you do not control the HTML markup.

You can easily remove an event listener by using the removeEventListener() method.

Syntax

element.addEventListener(event, function, useCapture);

The first parameter is the type of the event (like “click” or “mousedown” or any other HTML DOM Event.)

The second parameter is the function we want to call when the event occurs.

The third parameter is a boolean value specifying whether to use event bubbling or event capturing. This parameter is optional.

Note that you don’t use the “on” prefix for the event; use “click” instead of “onclick“.

Add an Event Handler to an Element

Example

Alert “Hello World!” when the user clicks on an element:

element.addEventListener(“click”, function(){ alert(“Hello World!”); });

You can also refer to an external “named” function:

Example

Alert “Hello World!” when the user clicks on an element:

element.addEventListener("click", myFunction);

function myFunction() {
  alert ("Hello World!");
}

Add Many Event Handlers to the Same Element

The addEventListener() method allows you to add many events to the same element, without overwriting existing events:

Example

element.addEventListener("click", myFunction);
element.addEventListener("click", mySecondFunction);

You can add events of different types to the same element:

Example

element.addEventListener("mouseover", myFunction);
element.addEventListener("click", mySecondFunction);
element.addEventListener("mouseout", myThirdFunction);

Add an Event Handler to the window Object

The addEventListener() method allows you to add event listeners on any HTML DOM object such as HTML elements, the HTML document, the window object, or other objects that support events, like the xmlHttpRequest object.

Example

Add an event listener that fires when a user resizes the window:

window.addEventListener("resize", function(){
  document.getElementById("demo").innerHTML = sometext;
});

Passing Parameters

When passing parameter values, use an “anonymous function” that calls the specified function with the parameters:

Example

element.addEventListener("click", function(){ myFunction(p1, p2); });

Event Bubbling or Event Capturing?

There are two ways of event propagation in the HTML DOM, bubbling and capturing.

Event propagation is a way of defining the element order when an event occurs. If you have a <p> element inside a <div> element, and the user clicks on the <p> element, which element’s “click” event should be handled first?

In bubbling the inner most element’s event is handled first and then the outer: the <p> element’s click event is handled first, then the <div> element’s click event.

In capturing the outer most element’s event is handled first and then the inner: the <div> element’s click event will be handled first, then the <p> element’s click event.

With the addEventListener() method you can specify the propagation type by using the “useCapture” parameter:

addEventListener(event, function, useCapture);

The default value is false, which will use the bubbling propagation, when the value is set to true, the event uses the capturing propagation.

Example

document.getElementById("myP").addEventListener("click", myFunction, true);
document.getElementById("myDiv").addEventListener("click", myFunction, true);

The removeEventListener() method

The removeEventListener() method removes event handlers that have been attached with the addEventListener() method:

Example

element.removeEventListener("mousemove", myFunction);

JavaScript HTML DOM Events

HTML DOM allows JavaScript to react to HTML events.

Reacting to Events

A JavaScript can be executed when an event occurs, like when a user clicks on an HTML element.

To execute code when a user clicks on an element, add JavaScript code to an HTML event attribute:

onclick=JavaScript

Examples of HTML events:

When a user clicks the mouse
When a web page has loaded
When an image has been loaded
When the mouse moves over an element
When an input field is changed
When an HTML form is submitted
When a user strokes a key

Continue reading JavaScript HTML DOM Events

JavaScript HTML DOM Animation

Learn to create HTML animations using JavaScript.

A Basic Web Page

To demonstrate how to create HTML animations with JavaScript, we will use a simple web page:

Example

<!DOCTYPE html>
<html>
<body>

<h1>My First JavaScript Animation</h1>

<div id="animation">My animation will go here</div>

</body>
</html>

Create an Animation Container

All animations should be relative to a container element. Continue reading JavaScript HTML DOM Animation