Can someone explain this code line to me?

Hi everyone, I am relatively new to JS and I am hoping someone could
tell me what this line of codes mean. This was written by some
brilliant guys at webfx and I am trying to understand some of their
codes.

To begin with I don't understand how this variable is set.

var sliderE1=document.getElementByID?
document.getElementById("slider-1"): null;

Question 1: What is the function of the "?" mark after the
document.getElementByID
Question 2: What is the reason for including ": null"
and Question 3: Can't this be done just by simply using
"document.getElementById("slider-1")"?

Thanks in advance.

wrote on 03 apr 2005 in comp.lang.javascript:

Hi everyone, I am relatively new to JS and I am hoping someone could
tell me what this line of codes mean. This was written by some
brilliant guys at webfx and I am trying to understand some of their
codes.

To begin with I don't understand how this variable is set.

var sliderE1=document.getElementByID?
document.getElementById("slider-1"): null;

Question 1: What is the function of the "?" mark after the
document.getElementByID
Question 2: What is the reason for including ": null"

var condition = false
var a = (condition) ? "This is true" : "This however is false"
alert(a)

will show: This however is false

var condition = true
var a = (condition) ? "This is true" : "This however is false"
alert(a)

will show: This is true

=========================================

and Question 3: Can't this be done just by simply using
"document.getElementById("slider-1")"?

(document.getElementByID)

is only true in browsers that support it.
in other [read older] browsers:

var sliderE1 = document.getElementById("slider-1")

would give an error and the js would stop.

========================================

Your first questions are so basic,
that I suppose you did not read any javascript tutorial before asking.

<http://www.google.com/search?q=javascript.tutorial>

--
Evertjan.
The Netherlands.
(Replace all crosses with dots in my emailaddress)