JavaScript HTML DOM 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:

• 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

In this example, the content of the element is changed when a user clicks on it:

Example

Click on this text!

In this example, a function is called from the event handler:

Example

Click on this text!

HTML Event Attributes

To assign events to HTML elements you can use event attributes.

Example

Assign an onclick event to a button element:

In the example above, a function named displayDate will be executed when the button is clicked.

Assign Events Using the HTML DOM

The HTML DOM allows you to assign events to HTML elements using JavaScript:

Example

Assign an onclick event to a button element:

In the example above, a function named displayDate is assigned to an HTML element with the id=»myBtn» .

The function will be executed when the button is clicked.

The onload and onunload Events

The onload and onunload events are triggered when the user enters or leaves the page.

The onload event can be used to check the visitor’s browser type and browser version, and load the proper version of the web page based on the information.

The onload and onunload events can be used to deal with cookies.

Example

The onchange Event

The onchange event is often used in combination with validation of input fields.

Below is an example of how to use the onchange. The upperCase() function will be called when a user changes the content of an input field.

Example

The onmouseover and onmouseout Events

The onmouseover and onmouseout events can be used to trigger a function when the user mouses over, or out of, an HTML element:

The onmousedown, onmouseup and onclick Events

The onmousedown , onmouseup , and onclick events are all parts of a mouse-click. First when a mouse-button is clicked, the onmousedown event is triggered, then, when the mouse-button is released, the onmouseup event is triggered, finally, when the mouse-click is completed, the onclick event is triggered.

More Examples

onmousedown and onmouseup
Change an image when a user holds down the mouse button.

onload
Display an alert box when the page has finished loading.

onfocus
Change the background-color of an input field when it gets focus.

Mouse Events
Change the color of an element when the cursor moves over it.

HTML DOM Event Object Reference

For a list of all HTML DOM events, look at our complete HTML DOM Event Object Reference.

Источник

Handling load events in a content document

JavaScript Event Handlers :Loading/ Unloading a Document

onBlur and onFocus Event Handlers

/* JavaScript Bible, Fourth Edition by Danny Goodman John Wiley & Sons CopyRight 2001

var alert("Element \"" + id + "\" has blurred.")

var alert("Element \"" + id + "\" has received focus.")

onBlur and onBlur Event Handlers

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Running a Script from the onLoad Event Handler

Using addBehavior() and removeBehavior()

/* JavaScript Bible, Fourth Edition by Danny Goodman John Wiley & Sons CopyRight 2001

var myPBehaviorID function turnOn()

myPBehaviorID = document.all.myP.addBehavior("makeHot.htc") setInitialColor()

if (document.all.myP.readyState == «complete») < var select = document.forms[0].colorChoice var color = select.options[select.selectedIndex].value document.all.myP.setHotColor(color) >else

document.all.myP.removeBehavior(myPBehaviorID)

> function setColor(select, color)
if (document.all.myP.hotColor) < document.all.myP.setHotColor(color) >else

var num = document.all.myP.behaviorUrns.length var msg = "The myP element has " + num + " behavior(s). " if (num > 0) < msg += "Name(s): \r\n" for (var i = 0; i < num; i++) < msg += document.all.myP.behaviorUrns[i] + "\r\n" >> alert(msg)

addBehavior() and removeBehavior() Method Lab

This is a sample paragraph. After turning on the behavior, it will turn your selected color when you mouse down anywhere in this paragraph.

Using Event Bubbling with the onClick Event

Using Event Bubbling

Using the fireEvent() Method

/* JavaScript Bible, Fourth Edition by Danny Goodman John Wiley & Sons CopyRight 2001

// assemble a couple event object properties function getEventProps()

var msg = "" var elem = event.srcElement msg += "event.srcElement.tagName: " + elem.tagName + "\n" msg += "event.srcElement.id: " + elem.id + "\n" msg += "event button: " + event.button return msg

> // onClick event handlers for body, myP, and mySPAN function bodyClick()

var msg = "Click event processed in BODY\n\n" msg += getEventProps() alert(msg) checkCancelBubble()

var msg = "Click event processed in P\n\n" msg += getEventProps() alert(msg) checkCancelBubble()

var msg = "Click event processed in SPAN\n\n" msg += getEventProps() alert(msg) checkCancelBubble()

> // cancel event bubbling if check box is checked function checkCancelBubble()

event.cancelBubble = document.controls.bubbleOn.checked

> // assign onClick event handlers to three elements function init()

document.body.onclick = bodyClick document.all.myP.onclick = pClick document.all.mySPAN.onclick = spanClick

> // invoke fireEvent() on object whose ID is passed as parameter function doFire(objID)

var newEvt = document.createEventObject() newEvt.button = 3 document.all(objID).fireEvent("onclick", newEvt) // don"t let button clicks bubble event.cancelBubble = true

fireEvent() Method

This is a paragraph (with a nested SPAN) that receives click events.

Источник

HTML DOM Body Object

You can access a element by using getElementsByTagName():

Example

Tip: You can also access a element by using the document.body property.

Create a Body Object

You can create a element by using the document.createElement() method:

Body Object Properties

Property	Description
aLink	Not supported in HTML5. See CSS :active Selector instead. Sets or returns the color of an active link in a document
background	Not supported in HTML5. Use style.backgroundImage instead. Sets or returns the background image for a document
bgColor	Not supported in HTML5. Use style.backgroundColor instead. Sets or returns the background color of a document
link	Not supported in HTML5. See CSS :link Selector instead. Sets or returns the color of unvisited links in a document
text	Not supported in HTML5. Use style.color instead. Sets or returns the color of the text in a document
vLink	Not supported in HTML5. See CSS :visited Selector instead. Sets or returns the color of visited links in a document

Standard Properties and Events

The Body object also supports the standard properties and events.

Related Pages

COLOR PICKER

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