Develop Reference

why doesn't this return an l-value?

Maybe ReSharper or visual studio is wrong, but I don't think that this returns an r-value. I also don't think it actually sets the property in the $parent controller:
function getParentItem(path) {
var obj = $scope.$parent;
var param = null;
var items = path.split(".");
for (var i = 0; i < items.length; i++) {
var item = items[i];
var split = item.split("(");
if (split.length === 2) {
param = split[1].replace(/[\)\']/g, "");
}
obj = obj[split[0]];
}
if (param == null) {
var thisObj = obj;
return thisObj;
} else {
return { obj: obj, param: param };
}
}
If I do this:
getParentItem($scope.someProperty) = "yadda"
I get error marked by probably ReSharper and I think it doesn't actually set the new value

As Amy/Volkan said your code is not valid but I think I get what you want to do. There are lots of ifs but here it goes:
if your $scope.someProperty is string property that you want to reassign on result of the function getParentItem, and your function returns object that can have that param ($scope.someProperty), first you need to figure out which path you pass in but it looks like it's some string separated by dots.
// so then assign result of the function to some variable
// you need to pass somePath to function
let parentItem = getParentItem(somePath);
// then change that property
parentItem[$scope.someProperty] = "yadda";
or another possibility what you might need would be:
parentItem.param[$scope.someProperty] = "yadda";
then do whatever you want with parentItem like put it on $scope or whatever.
If you want better help please do some jsfiddle or something.

The problem is (and I slap my head on how stupid I was) that the leaf branches of this $scope object aren't objects themselves, and in some cases in our code they don't even exist yet. You get so used to $scope being an object you fail to realize that the final elements can't possibly be objects at least in Javascript.
So the solution was to pass the value that I wanted to set as a parameter:
function getParentItem(path, optionalValue)
On the final loop of the parent search, if optionalValue is passed, I can then set the value onto the object:
obj[--last parameter name--] = optionalValue;

Pushing variable to an array depending on the checkbox selected

I have an simple example here, the check boxes were already given by the framework we are using so it just checks weather it is checked or not(returns true or false). And I have three variables with different options that will be pushed in an array and gets removed when unchecked. By the way I have made it worked but I think there is more proper way to do this.
var chk1 = data.config.chk1; // returns true or false only
var chk2 = data.config.chk2; // same as above
var chk3 = data.config.chk3;
var settA = "settingsA";
var settB = "settingsB";
var settC = "settingsC";
if (chk1) {
arr.push(settA)
}
if (chk2) {
arr.push(settB)
}
if (chk3) {
arr.push(settC);
}
console.log(arr)

I would eidt your Object that contains the chk# keys (with true or false values) with the actual settings value instead. Then if its in the object you know its true. That way you can make your code easier to handle like so.
var Chks = data.config;
for(var key in Chks)
arr.push(Chks[key])
Now if your object contained data.config.chk3 = 'SettingsA' your array will contain 'SettingsA'.
Maybe this wont work for you, but as a rule of thumb if your repeating the same commands over and over you should probably abstract, like use an itterator.

String variable prefixed with undefined in for loop

I have a drop-down on which i use .Change() to trigger a function. Function basically get certain data using getJSON and based on those value in have to create string of array for mp3 file.
Below code is generating string but always prefix undefined to string.
In code you will notice setTimeout which is just to provide certain delay till data received. In below example i am using static value and it still prefix undefined. not sure why may be i have defined variable in wrong manner.
Complete example JSBin
$('.customSurah').change(function(){
//surahNo = $('#surah option:selected').val();
setTimeout(function(){
//countSpan = $('#surah-wrapper').children().length;
surahNo = 1;
countSpan = 7;
var i=0;
for (i = 0; i <= countSpan; i++) {
strCat += surahNo+"/"+i+".mp3,";
console.log(strCat);
}
}, 3000);
});
OUTPUT
undefined114/0.mp3,
undefined114/0.mp3,114/1.mp3,
undefined114/0.mp3,114/1.mp3,114/2.mp3,
undefined114/0.mp3,114/1.mp3,114/2.mp3,114/3.mp3,
undefined114/0.mp3,114/1.mp3,114/2.mp3,114/3.mp3,114/4.mp3,
undefined114/0.mp3,114/1.mp3,114/2.mp3,114/3.mp3,114/4.mp3,114/5.mp3,
undefined114/0.mp3,114/1.mp3,114/2.mp3,114/3.mp3,114/4.mp3,114/5.mp3,114/6.mp3,

You have a variable strCat that is not initialized, and then you append a value to it in this line:
strCat += surahNo+"/"+i+".mp3,";
Since strCat is not initialized in first round of loop, you get undefined prepended to your string.
To fix this, you need to initialize the variable to empty value first:
var strCat = ''; // <- initialize your variable to empty value
surahNo = 1;
countSpan = 7;

The outcome is perfectly valid as per javascript is concerned.
Why?
I guess you probably know if you declare any variable in javascript and you don't assign its default value then automatically undefined is assigned. So, that is a valid. What happens when you do that:
var somevar; // non assigned default value set to -> undefined
console.log(somevar); // logs undefined
But,
In your case you have to give it a default value like a blank string var strCat "";. So, now when you do this:
var somevar = ""; // assigned default value to set to -> ""
console.log(somevar); // logs ""
So, the solution to your issue is, you have to initialize/assign a default value to your variable. like:
var strCat = "";

How to detect if a user input has been repeated?

I'm trying to make hangman in javascript and I want to check if the user has used a letter already. I made a var letterGuessValue = to 0 and if they add an input it = 1. I know this would say know to everything if i got it to work (it doesn't even do anything) but am I on the right track maybe? Here's my code. http://jsbin.com/aWOnAfe/5/edit

I would say add an input to a list and whenever they add another input (aka letter), check this list to see if it is already in there. If it is, then its because they've already used that letter before. If not, then it is a new letter.

I don't see where the difficult part is.
http://jsfiddle.net/DerekL/jgqQ9/
Sample code
var used = {};
$("input").keyup(function(){
var val = this.value;
alert( used[val] ? "Used" : "Not used" );
this.value = "";
used[val] = true;
});
How it works
Assign true to used.LETTER when a letter is entered. Before assigning it though, if it was undefined then it hasn't been used. If it is true then it is used.
Sometimes developers tend to use an Array to record pressed keystrokes when doing key combinations, but in this case, iterating an Array would require both more memory and computation power. A simple object is an enough fit.

Use an array to store all of the used letters and function like this to add new ones.
var inputs = []
function addLetter(letter){
var used = false;
for(var i = 0; i < inputs.length; i++){
if(inputs[i] == letter){
used = true;
break;
}
}
if(!used){
inputs.push(letter);
}
}

The easiest way is to append each letter to a string, like this:
var letters = '';
var letterPressed = 'X'; // uppercase it if appropriate for your language
if (letters.indexOf(letterPressed) > -1)
{
// you already pressed it
}
else
{
letters += letterPressed;
}
You can also use an array to store your list of presses, although IMO that's overkill.

Greasemonkey testing if array element exists

I'm writing a script that adds labels to things on a page using an element from an array based on part of the link... so my array looks like this:
var componentList[9] = "Sunnyseed"
var componentList[10] = "Echoberry"
var componentList[11] = "Riverstone"
var componentList[13] = "Auraglass"
var componentList[14] = "Skypollen"
You'll notice there is no '12'... I want the label to be 'Unknown' when the array item doesn't exist. Now, I can't exactly test my solution since I can't cause the target page to throw me a 12... so I was hoping somebody would tell me whether this will do what I want or not...
var component = ""
if(typeof componentList[critterIDval] == 'undefined'){
component="Unknown"
}
else{
component=componentList[critterIDval]
}
This is obviously not the full script, but it should be the important stuff... I just want to know if that will make it say 'Unknown' when the critterIDval is 12 - since it could take years to come across the situation for testing.

You're pretty much there. You're using a single-equals sign in your comparison, so that will mess it up, and I'm not sure you can create a JS array like that, but aside from that, you're good.
Here is the test I ran for it:
var componentList = [];
componentList[9] = "Sunnyseed";
componentList[10] = "Echoberry";
componentList[11] = "Riverstone";
componentList[13] = "Auraglass";
componentList[14] = "Skypollen";
for (var critterIDval = 9; critterIDval < 15; critterIDval++) {
if (typeof componentList[critterIDval] == 'undefined') { // double equals here
component = "Unknown";
} else {
component = componentList[critterIDval];
}
console.log(component);
}

It looks fine.
Though if you are sure that the value will never be an empty string(like componentList[14] = '';) then you can try
var component = componentList[critterIDval] || 'Unknown'

I want the label to be 'Unknown' when the array item doesn't exist.
The typeof operator does not tell you if a property exists or not as it returns undefined when the property doesn't exist but also when it does exist and has been assigned a the value undefined or simply created but hasn't been assigned a value.
There are two primary ways to test for the existence of a property: the in operator, which also looks on the [[Prototype]] chain and the hasOwnProperty method of all Objects. So
if (componentList.hasOwnProperty(critterIDval)) {
component = "Unknown"
} else {
component = componentList[critterIDval]
}
which you could also write as:
component = componentList.hasOwnProperty(critterIDval)? componentList[critterIDval] : 'unknown';
PS. there are other methods, such as looking at Object.keys(componentList) and componentList.propertyIsEnumerable(critterIDval), but the above are the most common.
Edit
If your requirement is not just to test for property existence but to also test for a "truthy" value, then:
if (componentList[critterIDval])
may be sufficient and will return false where the value is '' (empty string), 0, false, NaN, undefined or null.
Maybe just testing for a non–empty string or number will do:
if (/.+/.test(componentList[critterIDval]))
but that returns true for NaN, null and so on. So you need to specify what you are actually testing for, otherwise you may get undesired results for some values.