Develop Reference

how to increment a let variable without calling/creating a listerner function

In javascript we have addEventlister, this listens to an even and calls a function called a listener function. Is an alternate approach possible where we increment the value of a "let variable" without using a function to do this in case of event being triggered?
Instead of this
let clickVar = 0;
x.addEventListener("click", RespondClick);
function RespondClick() {
clickVar++;
}
Sample Alternate implementation
x.addEventListner(click);
if (event == true){ clickVar++; }
======Edit======
Responding to the comment
The more I read this, the more it seems like an XY problem - is there something else you are trying to solve?`
In my view, the second approach is more intuitive. i.e. why create a function unless it's absolutely necessary.
Responding to the comment
There is no logic to how the second approach. The code you write will be executed once. If you want to run code more than once, you have to call a function. In order to run a function when an event happens, you need an event listener.
This simple amendment should take care of the one-time calling problem.
x.addEventListner(click);
if (event == true){ clickVar++; event=false; }
But the point I am trying to make is function could have been avoided, the code could be easy enough to speak, not only write.

Your second sample doesn't work. That simply isn't how event listeners work. You must use a callback function. If you think the first sample is too verbose, you can use an anonymous function:
let clickVar = 0;
x.addEventListener("click", function() {
clickVar++;
});
Or an arrow function in more modern versions of Javascript
x.addEventListener("click", () => {
clickVar++;
});

assertExists with if-else statement

I use this code:
var x = require('casper').selectXPath;
...
casper.waitForSelector(x("//a[contains(#id,'cell_13_1')]"), function() {
this.test.assertExists(x("//a[contains(#id,'cell_13_1')]"), 'Clickable');
this.click(x("//a[contains(#id,'cell_13_1')]"));
});
I am trying to use if-else with assertExists to click another element if the first is not there:
casper.waitForSelector(x("//a[contains(#id,'cell_13_1')]"), function() {
if(this.test.assertExists(x("//a[contains(#id,'cell_13_1')]")==="PASS"){
this.click(x("//a[contains(#id,'cell_11_1')]"));}
else{
this.click(x("//a[contains(#id,'cell_22_1')]"));
}
});
But that does not seem to work. How would one do it correctly?

That's exactly what casper.exists() is for. You can also explicitly pass or fail some things:
casper.waitForSelector(x("//a[contains(#id,'cell_13_1')]"), function() {
if(this.exists(x("//a[contains(#id,'cell_13_1')]")){
this.test.pass("Clickable");
this.click(x("//a[contains(#id,'cell_11_1')]"));
} else {
this.test.fail("Clickable");
//this.click(x("//a[contains(#id,'cell_22_1')]"));
}
});
This code is equivalent to your first snippet. Comment the fail() call and uncomment the last click in order to get your "intended" behavior.
Btw, it doesn't make sense to fail some assertion and still continue with the script. You have to think about what exactly you want to test and what part of your script is supposed to be navigation to the component under test.

jQuery function in two events

I have this code:
$('#email').keyup(function() {
if(true || false)) {
} else {
}
});
I need include this function also in blur event.
I've tried to create a jquery function but I could not. Somebody give me a light.

You can do this -
$('#email').on('keyup blur',function() {
http://api.jquery.com/on/

Use the on method to attach multiple events, which are specified in the first argument passed to the function.
$('#email').on('keyup blur', function() {
if(true || false) { //there was an extra ) here
} else {
}
});
Working Example http://jsfiddle.net/nv39M/
One thing to be aware of, the keyup event is going to fire prior to the blur event firing.

Make a separate function as follows
function funcName(){
//Your code
}
Now,use jQuery on
$("#email").on("keyup",funcName);
$("#email").on("blur",funcName);
For reference,check
http://api.jquery.com/on/

There are (at least) two ways you could achieve this.
Specify multiple, space separated events as the first argument:
$('#email').on('keyup blur',function() {
// your logic
});
Use a named function:
function yourFunction() {
// your logic
}
$('#email').on('keyup', yourFunction);
$('#email').on('blur', yourFunction);
Option 1 is probably the best choice assuming you don't want to use the function anywhere else, and that you want to bind the event handlers at the same time. If, however, you wanted to bind the blur event at a later point (perhaps in response to another event), or to a different element, then the named function method would be the best choice.

How can I turn this javascript into a function? Is it already a function? A few very basic questions about js structure

I am learning javascript, and am trying to adjust the following:
$('#myform').change(function() {
if ($('#sv_I4b').attr('checked')||$('#sv_I4c').attr('checked')){
$('#sv_I5').removeClass('hidden');
} else {
$('#sv_I5').addClass('hidden');
}
});
To be a a function with a name that I can call on different events, such as page load etc.
I don't yet fully understand each element, but I know that:
if ($('#sv_I4b').attr('checked')||$('#sv_I4c').attr('checked')){
$('#sv_I5').removeClass('hidden');
} else {
$('#sv_I5').addClass('hidden');
}
is the core "logic" of the function: if (condition) {then this} else {that}
and more or less understand what is happening there. Which leaves the bounding javascript (is there better terminology than that?):
$('#myform').change(function() {...});
My Questions (are the following true etc):
The dollar I think denotes that it is jQuery
The id my form obviously
pertains the script to events within that form (namespace?)
.change seems to be, a trigger that listens to ... any change taking place
within #myform? so every time a change happens within #myform this
runs? That seems inefficient
function() I don't yet understand what
an anonymous or empty function does, just defines what is contained
in {} as a function?
My goal: to be able to have something like
function myfunction()
{
if ($('#sv_I4b').attr('checked')||$('#sv_I4c').attr('checked')){
$('#sv_I5').removeClass('hidden');
} else {
$('#sv_I5').addClass('hidden');
}
}
and then
$(function() {myfunction});
so I can call that function on page load, but I don't wan't to loose the functionality the .change syntax is providing me (that it changes as the user interacts with the elements on the page also.
Apologies for the general and cumbersome levels of ignorance

You guessed how to define the function correctly — that is,
function myfunction()
{
if ($('#sv_I4b').attr('checked')||$('#sv_I4c').attr('checked')){
$('#sv_I5').removeClass('hidden');
} else {
$('#sv_I5').addClass('hidden');
}
}
works just fine. However, this:
$(function() {myfunction});
Should be written as:
$(myfunction); // Run on page load.
$('#myform').change(myfunction); // ...and also run it when the form changes.
However, that second line won't actually work until the page has loaded unless the form exists at the time the script runs, so you may want to change it to this:
$(function() { // On page load, run this anonymous function:
myfunction(); // Run the function now (where now, at this point, is page load).
$('#myform').change(myfunction); // ...as well as when the form changes.
});

$ is shorthand notation for jQuery, and essentially namespaces any functions to the jQuery framework.
my_form is a DOM selector. $('#my_form') wraps the matched DOM element up as a jQuery object, adding all sorts of useful methods and properties.
.change() is an event listener which, as you guessed, watches for change events on that jQuery object. It is a little inefficient - take a look .on() instead.
the most useful behaviour an anonymous function (closure) is to create private scope, something that javascript doesn't otherwise provide.

How do I throttle in jQuery only on a certain condition, and execute immediately otherwise?

I'm using this jQuery plug-in for throttle support.
I have a text input variable called textbox set as follows, which will execute someFunction at most once every second:
textbox.keypress($.throttle(1000, someFunction(e)));
However, I want someFunction to execute immediately if the key pressed is the enter key. I'm not quite sure how to do this. Any suggestions?

textbox.keypress(function(event) {
if(event.which == 13){
// Enter key has been preseed. Do something.
} else {
$.throttle(1000, function(){
someFunction(event);
})
}
});
Keep in mind what you're passing for callbacks. Both 'someFunction' and '$.throttle' are being invoked directly, with their return values being passed as callbacks. To avoid this, wrap the functions in a function (lambda) as I have done above.

You will need to have in your code a handler for the 'ENTER' keypress and abort the $.throttle if that is the case. Can you paste more of your code maybe to give us a better idea of what to work with?