Javascript DOM 2 - lecture and study notes PDF

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JavaScript HTML DOM

http://www.w3schools.com/js/js_htmldom_methods.asp With the HTML DOM, JavaScript can access and change all the elements of an HTML document. The HTML DOM (Document Object Model) When a web page is loaded, the browser creates a Document Object Model of the page. The HTML DOM model is constructed as a tree of Objects:

The HTML DOM Tree of Objects

With the object model, JavaScript gets all the power it needs to create dynamic HTML: • JavaScript can change all the HTML elements in the page • JavaScript can change all the HTML attributes in the page • JavaScript can change all the CSS styles in the page • JavaScript can remove existing HTML elements and attributes • JavaScript can add new HTML elements and attributes • JavaScript can react to all existing HTML events in the page • JavaScript can create new HTML events in the page What is the DOM? The DOM is a W3C (World Wide Web Consortium) standard. The DOM defines a standard for accessing documents: "The W3C Document Object Model (DOM) is a platform and language-neutral interface that allows programs and scripts to dynamically access and update the content, structure, and style of a document."

What is the HTML DOM? The HTML DOM is a standard object model and programming interface for HTML. It defines: • The HTML elements as objects • The properties of all HTML elements • The methods to access all HTML elements • The events for all HTML elements In other words: The HTML DOM is a standard for how to get, change, add, or delete HTML elements.

JavaScript - HTML DOM Methods HTML DOM methods are actions you can perform (on HTML Elements). HTML DOM properties are values (of HTML Elements) that you can set or change. The DOM Programming Interface The HTML DOM can be accessed with JavaScript (and with other programming languages). In the DOM, all HTML elements are defined as objects. The programming interface is the properties and methods of each object. A property is a value that you can get or set (like changing the content of an HTML element). A method is an action you can do (like add or deleting an HTML element). Example The following example changes the content (the innerHTML) of the element with id="demo":



In the example above, getElementById is a method, while innerHTML is a property. The getElementById Method The most common way to access an HTML element is to use the id of the element. In the example above the getElementById method used id="demo" to find the element.

The innerHTML Property The easiest way to get the content of an element is by using the innerHTML property. The innerHTML property is useful for getting or replacing the content of HTML elements. The innerHTML property can be used to get or change any HTML element, including and .

JavaScript Where To JavaScript can be placed in the and the sections of an HTML page. The tags.

Older examples may use a type attribute: You can place an external script reference in or as you like. The script will behave as if it was located exactly where the

Using document.write() For testing purposes, it is convenient to use document.write():

My First Web Page My first paragraph.

Using document.write() after an HTML document is fully loaded, will delete all existing HTML:

My First Web Page My first paragraph.

Try it

The document.write() method should be used only for testing. Using innerHTML To access an HTML element, JavaScript can use the document.getElementById(id) method. The id attribute defines the HTML element. The innerHTML property defines the HTML content:

My First Web Page My First Paragraph

To "display data" in HTML, (in most cases) you will set the value of an innerHTML property.

Using console.log() In your browser, you can use the console.log() method to display data. Activate the browser console with F12, and select "Console" in the menu.

My First Web Page My first paragraph.



JavaScript Events: HTML Events http://www.w3schools.com/js/js_events.asp 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 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 ... 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:

With double quotes:

In the following example, an onclick attribute (with code), is added to a button element: the JavaScript code changes the content of the element with id="demo".

The time is?

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

The time is? JavaScript code is often several lines long. It is more common to see event attributes calling

functions:

Click the button to display the date. The time is?



HTML DOM Events http://www.w3schools.com/jsref/dom_obj_event.asp HTML DOM events allow JavaScript to register different event handlers on elements in an HTML document. Events are normally used in combination with functions, and the function will not be executed before the event occurs (such as when a user clicks a button). Common HTML Events Here is a list of some common HTML events: Event Description onchange An HTML element has been changed onclick The user clicks an HTML element onmouseover The user moves the mouse over an HTML element onmouseout The user moves the mouse away from an HTML element onkeydown The user pushes a keyboard key onload The browser has finished loading the page The list is much longer: W3Schools JavaScript Reference HTML DOM Events.

JavaScript HTML DOM - Changing HTML http://www.w3schools.com/js/js_htmldom_html.asp The HTML DOM allows JavaScript to change the content of HTML elements. Changing the HTML Output Stream JavaScript can create dynamic HTML content: Date: Fri Oct 16 2015 11:57:33 GMT+0200 (CEST)

In JavaScript, document.write() can be used to write directly to the HTML output stream:



Never use document.write() after the document is loaded. It will overwrite the document.

Changing HTML Content The easiest way to modify the content of an HTML element is by using the innerHTML property. To change the content of an HTML element, use this syntax: document.getElementById(id).innerHTML = new HTML One of many HTML methods is getElementById(). This example uses the method to "find" an HTML element (with id="demo" ), and changes the element content (innerHTML) to "Hello JavaScript":

What Can JavaScript Do? JavaScript can change HTML content.

Click Me!

This example changes the content of an element:

Old Header

Example explained: • The HTML document above contains an element with id="header" • We use the HTML DOM to get the element with id="header" • A JavaScript changes the content (innerHTML) of that element

Changing the Value of an Attribute To change the value of an HTML attribute, use this syntax: document.getElementById(id).attribute=new value For example, to change an HTML element from text input to radio button element, by changing the type attribute of an tag:

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This example changes the value of the src attribute of an element:



Example explained: • The HTML document above contains an element with id="myImage" • We use the HTML DOM to get the element with id="myImage" • A JavaScript changes the src attribute of that element from "smiley.gif" to "landscape.jpg"

JavaScript HTML DOM - Changing CSS http://www.w3schools.com/js/js_htmldom_css.asp The HTML DOM allows JavaScript to change the style of HTML elements. Changing HTML Style To change the style of an HTML element, use this syntax: document.getElementById(id).style.property=new style The following example changes the style of a element:

Hello World!

The paragraph above was changed by a script.

Changing the style of an HTML element, is a variant of changing an HTML attribute:

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Promijeni font

Promijeni font u 55px.

JavaScript Can Validate Data JavaScript is often used to validate input in forms.



JavaScript Can Validate Input Please input a number between 1 and 10:

Submit

Did You Know? JavaScript and Java are completely different languages, both in concept and design. JavaScript was invented by Brendan Eich in 1995, and became an ECMA standard in 1997. ECMA-262 is the official name. ECMAScript 6 (released in June 2015) is the latest official version of JavaScript....