dialog boxes in javascript events in javascript – what are they – “which events are there?”...
TRANSCRIPT
• Dialog boxes in JavaScript• Events in JavaScript
– What are they– “Which events are there?”– “How do I register event handlers to an HTML element?”– “Once I have successfully accessed the event, how do I read out
its properties?”
Topic 5_3: Interacting with the user
By the end of this lecture you should :
Topic 5_3: Interacting with the user
Dialog boxes:
Three methods used by the window object to interact with the user:
- alert( ) example 1, example 2- prompt( ) example 3- Confirm( ) example 4
Dialog boxes in JavaScriptEvents in JavaScript
What are they“Which events are there?”
“How do I register event handlers to an HTML element?”
“Once I have successfully accessed the event, how do I read out its properties?
Topic 5_3: Interacting with the user
Events – building blocks of interactivity:
Object that generates an
event (e.g. button)
Event handlers supported by
the object (e.g. onclick)
Custom event handler function may be assigned
to the evente.g. function
buttonPressed(){//do
something}
When the user does something an event takes place.An event handler waits until the event takes place and then executes the script you have defined – this is the core of interactivity.
http://www.quirksmode.org/js/introevents.html - an excellent resource for understanding events in detail
Dialog boxes in JavaScriptEvents in JavaScript
What are they“Which events are there?”
“How do I register event handlers to an HTML element?”
“Once I have successfully accessed the event, how do I read out its properties?
Topic 5_3: Interacting with the user
Events:“How should I write an event handling script?”
“Which events are there?”
http://www.w3schools.com/jsref/dom_obj_event.asp
Dialog boxes in JavaScriptEvents in JavaScript
What are they“Which events are there?”
“How do I register event handlers to an HTML element?”
“Once I have successfully accessed the event, how do I read out its properties?
Topic 5_3: Interacting with the user
Events:“How should I write an event handling script?”
“How do I register event handlers to an HTML element?”
Traditionally,
element.onclick = doSomething;
Whenever the user clicks on the HTML element, the function doSomething() is executed.
Note that in the registration of an event handler you do not use parentheses ()
Dialog boxes in JavaScriptEvents in JavaScript
What are they“Which events are there?”
“How do I register event handlers to an HTML element?”
“Once I have successfully accessed the event, how do I read out its properties?
Topic 5_3: Interacting with the user
Events:“How should I write an event handling script?”Dialog boxes in JavaScriptEvents in JavaScript
What are they“Which events are there?”
“How do I register event handlers to an HTML element?”
“Once I have successfully accessed the event, how do I read out its properties?
For example, for a click event can write something like this
element.onclick = doSomething; another_element.onclick = doSomething; function doSomething() { this.style.backgroundColor = '#cc0000'; }
this always refers to the “owner” of the function we're executing, or rather, to the object that a function
is a method of.
If we were to executefunction doSomething() {
this.style.color = '#cc0000'; }without other preparation we would get an error. Why?
What else do we need to do to correctly structure code and avoid the error?
Topic 5_3: Interacting with the user
Events:“How should I write an event handling script?”
A brief note about w3C event handling:
- Key method is the addEventListener()- Takes three arguments
- Event type- Function to be executed - Boolean value (True or false)
To register doSomething() function to the onclick of an element :element.addEventListener('click',doSomething,false)
To removeelement.removeEventListener('click',doSomething,false)
Dialog boxes in JavaScriptEvents in JavaScript
What are they“Which events are there?”
“How do I register event handlers to an HTML element?”
“Once I have successfully accessed the event, how do I read out its properties?
Topic 5_3: Interacting with the user
Events:“How should I write an event handling script?”
Using anonymous functions for event handling:
For example:
element.addEventListener('click',function () { this.style.backgroundColor = '#cc0000' },false)
What is the boolean value about?
Dialog boxes in JavaScriptEvents in JavaScript
What are they“Which events are there?”
“How do I register event handlers to an HTML element?”
“Once I have successfully accessed the event, how do I read out its properties?
Topic 5_3: Interacting with the user
Events:“How should I write an event handling script?”Event order
The boolean value we see in the W3C event listener on the previous slide refers to order of events.
Netscape
Microsoft
W3C
Dialog boxes in JavaScriptEvents in JavaScript
What are they“Which events are there?”
“How do I register event handlers to an HTML element?”
“Once I have successfully accessed the event, how do I read out its properties?
Topic 5_3: Interacting with the user
Events:“How should I write an event handling script?”
What is the type of the event?
Which key is being pressed?
Dialog boxes in JavaScriptEvents in JavaScript
What are they“Which events are there?”
“How do I register event handlers to an HTML element?”
“Once I have successfully accessed the event, how do I read out its properties?