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simplify if else statement

I have some functionality dependent on many conditions. All variables in conditional statements are boolean variables and the code is the following and I don't like it:
if (userHasMoreThanOneMarket && isOnlyMarketSelected || !userHasMoreThanOneMarket && userHasMoreThanOneAgency) {
if (isOnlyAgencySelected) {
//do case 1
} else if (noAgencySelected && isOnlyMarketSelected) {
//do case 2
}
}
Is there a way to make it more understandable and nice?

That's about as concise as you're going to get with JavaScript. I suppose if you really wanted to, you could create variables to store your binary options:
var multiMarketOneSelected = userHasMoreThanOneMarket && isOnlyMarketSelected;
var singleMarketMultiAgency = !userHasMoreThanOneMarket && userHasMoreThanOneAgency;
if (multiMarketOneSelected || singleMarketMultiAgency) {
if (isOnlyAgencySelected) {
//do case 1
} else if (noAgencySelected && isOnlyMarketSelected) {
//do case 2
}
}
Though I don't really know if you gain much readability from that.

Your code seems fine, but if you don't like it you could do something like this (note that the only improvement here is style, if you like it better):
function check(){
return {
valid: userHasMoreThanOneMarket && isOnlyMarketSelected || !userHasMoreThanOneMarket && userHasMoreThanOneAgency,
case: [
isOnlyAgencySelected,
noAgencySelected && isOnlyMarketSelected
]
};
}
var conditions = check();
if (conditions.valid) {
if (conditions.case[0]) {
//do case 1
} else if (conditions.case[1]) {
//do case 2
}
}

Some things I would try to make the code more readable:
Initialise the variables in a way that you don't have to negate them again. So !userHasMoreThanOneMarket becomes userHasOneMarket
isOnlyMarketSelected sounds redundant to me. And you are checking it in the outer if-clause and the inner again.
You probably have a lot of code above this code snippet to initialise and set all this boolean values. Try return; statements after each variable to get rid of if-conditions.
I hope this helps.

Ternary Operators as short conditional statements

Is there anything wrong with using ternary operators in place of longer conditional statements in Javascript, for instance using:
(variable == "dog") ? dog_stuff() : false;
Rather than
if ( variable == "dog" )
{
dog_stuff();
}
This may sound like a stupid question but I just find it's pretty quick and easy to read, I just don't want to be using it if there's a possible drawback?

You could also write
(variable == 'dog') && dog_stuff();
if you don't have an else statement.
A few lines from backbone.js:
options || (options = {});
models = _.isArray(models) ? models.slice() : [models];
model = this.getByCid(models[i]) || this.get(models[i]);
You can group multiple statements, if it's very necessary:
(1==1) && (a=2,b=3)
alert(a); // 2
alert(b); // 3

It's wrong because you're telling your code to execute false. Imagine the following code:
if ( variable == "dog" )
{
dog_stuff();
} else {
false;
}
IMO the 4 line conditional function call is perfectly fine. You can shorthand it to:
if (variable == "dog") dog_stuff();
The only problem with this is if you comment it out, or add 1 more function then things look correct, but don't execute correctly:
if (variable == "dog") dog_walk(); dog_bark(); // dog_bark executes always!
if (variable == "dog") // dog_walk();
earn_cash(); // suddenly earn_cash() is dog-dependent.

As long as the format is easily understood by you and anyone else that may need to read the code, it's fine.

How to construct a string which will pass if(variable)

I'm a jquery novice. I've boiled my code down to the simplest way to describe my problem. But I am having trouble wording it.
if(var1 && var2){
// this works
}
searchMe = var1+" && "+var2;
if(searchMe){
// this doesn't work
}
searchMe = "var1"+" && "+"var2";
if(searchMe){
// still doesn't work
}
I would like to be able to construct that "searchMe" variable based on user input. Can someone tell me a better way to do this? Thanks!

Not sure but you can make use of eval function
if(eval(searchMe)){
// this doesn't work
}

A possible way to do this without the dreaded eval (which really, you should never use) is to just evaluate as you go, and then end up with one variable at the end which is boolean.
var a = true;
var b = a && (false || true) && (1 < 2);
if (b)
document.write('yes');
else
document.write('no');
var c = b && false;
document.write(', ');
if (c)
document.write('yes');
else
document.write('no');
To relate it to your example
searchMe = var1 && var2;
if(searchMe){
// this does work
}

Javascript OR in an IF statement

I am trying to make an if statement in javascript that will do something if the variable does not equal one of a few different things. I have been trying many different variations of the OR operator, but I cant get it to work.
if(var != "One" || "Two" || "Three"){
// Do Something
}
Any ideas? Thanks!
Update:
I have tried this before:
if(var != "One" || var != "Two" || var != "Three"){
// Do Something
}
For some reason it does not work. My variable is pulling information from the DOM i dont know if that would effect this.
Actual Code
// Gets Value of the Field (Drop Down box)
var itemtype = document.forms[0].elements['itemtype' + i];
if(itemtype.value != "Silverware" || itemtype.value != "Gold Coins" || itemtype.value != "Silver Coins"){
// Do Something
}

Your expression is always true, you need:
if(!(myVar == "One" || myVar == "Two" || myVar == "Three")) {
// myVar is not One, Two or Three
}
Or:
if ((myVar != "One") && (myVar != "Two") && (myVar != "Three")) {
// myVar is not One, Two or Three
}
And, for shortness:
if (!/One|Two|Three/.test(myVar)) {
// myVar is not One, Two or Three
}
// Or:
if (!myVar.match("One|Two|Three")) {
// ...
}
More info:
De Morgan's Laws
Edit: If you go for the last approaches, since the code you posted seems to be part of a loop, I would recommend you to create the regular expression outside the loop, and use the RegExp.prototype.test method rather than String.prototype.match, also you might want to care about word boundaries, i.e. "noOne" will match "One" without them...

Assuming you mean "val does not equal One or Two or Three" then De Morgan's Theorem applies:
if ((val != "One") && (val != "Two") && (val != "Three")) {
// Do something...
}

For a shorter way to do it, try this format (copied from http://snook.ca/archives/javascript/testing_for_a_v):
if(name in {'bobby':'', 'sue':'','smith':''}) { ... }
or
function oc(a)
{
var o = {};
for(var i=0;i<a.length;i++)
{
o[a[i]]='';
}
return o;
}
if( name in oc(['bobby', 'sue','smith']) ) { ... }

The method mentioned by Mike will work fine for just 3 values, but if you want to extend it to n values, your if blocks will rapidly get ugly. Firefox 1.5+ and IE 8 have an Array.indexOf method you can use like so:
if(["One","Two","Test"].indexOf(myVar)!=-1)
{
//do stuff
}
To support this method on IE<=7, you could define a method called Array.hasElement() like so:
Array.prototype.hasElement = function hasElement(someElement)
{
for(var i=0;i<this.length;i++)
{
if(this[i]==someElement)
return true;
}
return false;
}
And then call it like so:
if(!["One","Two","Three"].hasElement(myVar))
{
//do stuff
}
Note: only tested in Firefox, where this works perfectly.

In addition to expanding the expression into three clauses, I think you'd better name your variable something other than var. In JavaScript, var is a keyword. Most browsers aren't going to alert you to this error.

Alternate way using an array:
var selected = ['Silverware', 'Gold Coins', 'Silver Coins'];
if ( selected.indexOf( el.value ) != -1 ) {
// do something if it *was* found in the array of strings.
}
Note: indexOf isnt a native method, grab the snippet here for IE:
https://developer.mozilla.org/En/Core_JavaScript_1.5_Reference/Objects/Array/IndexOf

Is a JavaScript try-catch ignoring an expected occasional error bad practice?

In JavaScript is it wrong to use a try-catch block and ignore the error rather than test many attributes in the block for null?
try{
if(myInfo.person.name == newInfo.person.name
&& myInfo.person.address.street == newInfo.person.address.street
&& myInfo.person.address.zip == newInfo.person.address.zip) {
this.setAddress(newInfo);
}
} catch(e) {} // ignore missing args

If you expect a particular condition, your code will be easier to maintain if you explicitly test for it. I would write the above as something like
if( myInfo && newInfo
&& myInfo.person && newInfo.person
&& myInfo.person.address && newInfo.person.address
&& ( myInfo.person.name == newInfo.person.name
&& myInfo.person.address.street == newInfo.person.address.street
&& myInfo.person.address.zip == newInfo.person.address.zip
)
)
{
this.setAddress(newInfo);
}
This makes the effect much clearer - for instance, suppose newInfo is all filled out, but parts of myInfo are missing? Perhaps you actually want setAddress() to be called in that case? If so, you'll need to change that logic!

Yes. For one, an exception could be thrown for any number of reasons besides missing arguments. The catch-all would hide those cases which probably isn't desired.

I would think that if you're going to catch the exception then do something with it. Otherwise, let it bubble up so a higher level can handle it in some way (even if it's just the browser reporting the error to you).

On a related note, in IE, even though the specs say you can, you can not use a try/finally combination. In order for your "finally" to execute, you must have a catch block defined, even if it is empty.
//this will [NOT] do the reset in Internet Explorer
try{
doErrorProneAction();
} finally {
//clean up
this.reset();
}
//this [WILL] do the reset in Internet Explorer
try{
doErrorProneAction();
} catch(ex){
//do nothing
} finally {
//clean up
this.reset();
}

You could always write a helper function to do the checking for you:
function pathEquals(obj1, obj2, path)
{
var properties = path.split(".");
for (var i = 0, l = properties.length; i < l; i++)
{
var property = properties[i];
if (obj1 === null || typeof obj1[property] == "undefined" ||
obj2 === null || typeof obj2[property] == "undefined")
{
return false;
}
obj1 = obj1[property];
obj2 = obj2[property];
}
return (obj1 === obj2);
}
if (pathEquals(myInfo, newInfo, "person.name") &&
pathEquals(myInfo, newInfo, "person.address.street") &&
pathEquals(myInfo, newInfo, "person.address.zip"))
{
this.setAddress(newInfo);
}

For the example given I would say it was bad practice. There are instances however where it may be more efficient to simply trap for an expected error. Validating the format of a string before casting it as a GUID would be a good example.