AJAX

Question 1

What does the function “escape()” do in javascript?

Answer 1

Similar to filter_var, it cleans up the url to remove any characters that should not be there. (note this is deprecated)

Question 2

What should you use instead of escape()?

Answer 2

encodeURI or encodeURIComponent

Question 3

What function do you use to reverse the result of encodeURI?

Answer 3

decodeURI

Question 4

What function do we use to request a “request object”?

Answer 4

try {
   request = new XMLHttpRequest();
} catch (tryMS) {
  try {
    request = new ActiveXObject("Mxsml2.XMLHTTP");
  } catch (otherMS) {
    try {
      request = new   ActiveXObject("Microsoft.XMLHTTP");
    } catch (failed) {
       request = null;
    }
  }
}

Question 5

How do you configure a “request object” to retrieve information

Answer 5

var url = “getDetails.php?ImageID=” + encodeURI(itemName);

request. open(“GET”, url, true);
request. onreadystatechange = displayDetails;
request. send(null);

Question 6

What do the parameters in request.open call do?

Answer 6

request.open(Method, url, asynchronous);
Method - GET or POST
url - The url that will respond to the request
asynchronous - Is the request sync or async

Question 7

When assigning a function to a callback parameter do you include parenthesis?

Answer 7

No - you don’t include the parenthesis unless you are making a function call. i.e.
myCallback = coolCallback;

Question 8

What does the readyState property on the request object do?

Answer 8

Contains a value that represents the current state of the object

Question 9

What does the status property on the request object do?

Answer 9

Contains a status code returned by the server indicating success or if a requested resource is missing (i believe it can contain far more than this however).

Question 10

What does the property responseXML on the request object do?

Answer 10

Contains information sent back by the server in XML format (this is empty unless the server responds in XML)

Question 11

What does the statusText property on the request object do?

Answer 11

Provides the status code message returned by the server, i.e. OK for status 202.

Question 12

What does the responseText property on the request object do?

Answer 12

Contains textual information sent back by the server (this may be empty if the server sends the data back as XML).

Question 13

What value will the readyState property have when the server completes processing?

Answer 13

4 (starts at 0)

Question 14

What event do you use to make sure code is executed after the page is loaded

Answer 14

onload

Question 15

What event do you use to trigger code when an image or div on a page is clicked?

Answer 15

onclick

Question 16

What event do you use to determine when a user has clicked on an input box?

Answer 16

onfocus

Question 17

What event do you use to determine when a user has clicked out of an input box?

Answer 17

onblur

Question 18

What event do you use to test if a user has rolled over an image or div in a page?

Answer 18

onmouseover

Question 19

What event do you use to test if a user has moved the mouse from outside the dimensions of an image or div?

Answer 19

onmouseout

Question 20

What event is raised when a form is submitted?

Answer 20

onsubmit

Question 21

What event is raised when a window is resized?

Answer 21

onresize

Question 22

What event is raised if an image cannot be loaded?

Answer 22

onerror

Question 23

You can assign an event handler easily by using the ‘=’ sign, but what if you want to add more than one?

Answer 23

Use the function addEventListener
myBtn.addEventListener(p1, p2, p3)
p1 = event name (without 'on' in front)
p2 = the event handler
p3 = Use capture

Question 24

What level DOM is it when you are adding event handlers directly to controls?

Answer 24

DOM Level 0

Question 25

What level of DOM is it when you are adding event handlers via an interface?

Answer 25

DOM Level 2

Question 26

What order are event handlers called when added using addEventListener?

Answer 26

It isn’t guarenteed

Question 27

If an object called Tab has a property called onclick, and a function called showTab is assigned to it. To what does “this” refer to in the showTab function?

Answer 27

To the Tab object.

Question 28

In what situation should you avoid using “this” in javascript and why?

Answer 28

When writing event handlers (because I.E. deals with this differently when using attachEvent, DOM level 2).

Question 29

What should you use instead of using ‘this’ in an event handler?

Answer 29

Use the object passed to the handler

Question 30

What is an “activated object”?

Answer 30

An object on a page that has been triggered by an event (basically it’s the event object passed to a event handler in DOM level 2)

Question 31

What is one issue with request objects that must be taken into account when multiple requests are in play?

Answer 31

You must be careful that subsequent calls don’t trounce the first request object.