for (var i=0, y=0; i<5; i++, y+=2){
 document.write(i+" "+y+"<br />")
}

Output:

(condition)? exp1 : exp2

For example:

y=-1
x=(y<0)? 5: 10 //x contains 5

Mor example(s).

var myarray=['joe', 'mary', 'jane']
var boss={name: 'george'}
worker={name: 'peter'}
var x=3
y=4

delete myarray[1] //returns true, myarray[1] now undefined
delete boss //returns false, since boss is a declared variable
delete worker //returns true, since worker is an undeclared variable
delete x //returns false, since x is a declared variable
delete y //returns true, since y is an undeclared variable

var myarray=['joe', 'mary', 'jane']
var workers={worker1: 'peter', worker2: 'edward', worker3: 'john'}

"lastModified" in document //true, document.lastModified exists
"length" in myarray //true
"mary" in myarray //false, "mary" is an array value, not property (use array.indexOf() instead)
"worker1" in workers //true

Note that properties deleted using the "delete" operator above will return false when tested for using "in".

var today=new Date()
alert(today instanceof Date) //alerts true, today is a Date object

var mycars=["Honda", "Toyota", "Ford"
alert(mycars instanceof Array) //alerts true, mycars is an Array object

function house(w, h){
this.area=w*h
}
var myhouse=new house(100, 200)
alert(myhouse instanceof house) //alerts true

var today=new Date() //create new instance of Date object

function triangle(base, height){
 this.area=base*height/2
}
var bigtriangle=new triangle(200, 150) //create new instance of triangle object

try{
 somefunction()
 alert('I guess you do exist')
}
catch(e){
 alert('An error has occurred: '+e.message)
}

In the above, if "somefunction()" doesn't exist, the browser immediately skips the reminder of what's inside try() and executes the code inside catch().

There's another clause, finally, that if defined will be executed regardless of whether an error occurs in the try clause:

try{
 undefinedfunction()
 alert('I guess you do exist')
}
catch(e){
 alert('An error has occurred: '+e.message)
}
finally{
 alert('I am alerted regardless of the outcome above')
}

try should never be defined just by itself, but always followed by either catch, finally, or both. Within each clause, you can define additional try/catch/finally statements following the same aforementioned rule (nesting). Take the instance where an error has occurred within the catch clause- defining an additional try/catch statement inside it takes care of it:

var ajaxrequest=null
if (window.ActiveXObject){ //Test for support for different versions of ActiveXObject in IE
 try {
  ajaxrequest=new ActiveXObject("Msxml2.XMLHTTP")
 }
 catch (e){
  try{
   ajaxrequest=new ActiveXObject("Microsoft.XMLHTTP")
  } //end inner try
  catch (e){
   alert("I give up. Your IE doesn't support Ajax!")
  } //end inner catch
 } //end outer catch
}
else if (window.XMLHttpRequest) // if Mozilla, Safari etc
 ajaxrequest=new XMLHttpRequest()

ajaxrequest.open('GET', 'process.php', true) //do something with request

Here I'm using a nested try/catch statement to try and determine in IE which version of the ActiveX Object it supports that's needed to initialize an Ajax request. Using object detection won't work here, since the issue isn't whether the browser supports ActiveXObject here, but which version.

More info: "Handling runtime errors in JavaScript using try/catch/finally".

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